The key to playing rhythm and using the fist finger A is not to continue with wide-arc arm-swing strumming. You need to narrow the swinging arc and be more controlled in your picking, not hitting the thin e string so much either down or up. Not hitting it at all if you can.
Hope that helps.
Cheers 
| Richard_close2u | Community Moderator, Official Guide, JustinGuitar Approved Teacher
I struggled for over a week to get the mini barre A to work - I just couldnāt find a position where my index finger would give me the result (barre + muted E). Then on a whim I tried using my middle finger instead of index finger and boom!! Immediately it was a comfortable, natural position with the notes ringing out and the E muted. One more example of how finger anatomy varies from person to person.
Hi all, I was wondering if anyone has any tips for me about how I might manage to wrap my thumb around the back of the neck to mute the 6th string? I am a female human and my hands/fingers are potentially on the short side even then. 
Thanks
Hello @tmh and welcome to the Community.
Tom, can I strongly encourage, urge, you not to use your 2nd finger.
That is a habit that if you form it, you will regret it and find it limits your progress further down the line.
Use your index and develop that skill, even if occasionally to do not manage to mute the thin E string.
Hope that helps.
Cheers
| Richard_close2u | Community Moderator, Official Guide, JustinGuitar Approved Teacher
Hello @alexia79 and welcome to the Community.
If you were a female of a different species my answer might be different ā¦ haha 
For the beginning stages of this chord shape, do not worry too much about wrapping your thumb around to mute.
Just be a little more careful to strum from the A string only.
Hope that helps.
Cheers
| Richard_close2u | Community Moderator, Official Guide, JustinGuitar Approved Teacher
@alexia79 Iāve got pretty long fingers, but am also finding this challenging.
I started playing in a semi-classical position, which is great for barre chords, but this is not working very well for thumb muting.
Iām finding neck position makes a big difference. Keeping the neck lower and more angled away from my body is helping.
Also, you donāt need to hook your thumb over the top of the neck. As long as you can lightly touch the thick E string, it will not ring.
There are multiple ways your thumb and palm can interact with the back of the neck too.
You can just use the first joint of your thumb, or where the thumb meets the palm, or the whole palm.
Finding out what works best might be easier done standing up, with a strap. Then you can probably transfer that to playing seated.
Okayā¦ thank you for the feedback. Iāll take the direction you provide and work on using my index finger for the mini barre A. If you would be so kind, however, Iām curious about why using the middle finger is problematic so a bit more info on this would be appreciated. Regards, Tom
Hi Tom,
Personally, I think using your index finger makes changes to other A-shape barre chords (minor grips as well) much easier than using your middle finger. In the 1st scenario, youāll just have to move your index finger a string above, while in the 2nd scenario youāll need to rearrange the whole fingering.
Yes, the common change from A to F#m (and back) is much easier when you mini-barre the A with your index finger.
Also, as you advance, having the middle and ring fingers free for adding embellishments to the mini-barre A is very useful. The blues shuffle rhythm with the open A chord is an example of this.
Hi. When playing the mini bar for A, I end up pushing with my middle finger on top of my index finger. Is this wrong? Iāve done this for a number of years so Iām worried if this is a bad habit it will be hard to break.
Maybe you learned on, or are currently playing, a guitar with high action, and you need that extra pressure to make all the strings ring?
I canāt think of any specific problems this might cause, but usually any extra effort or complication will interfere with your playing at some point.
I agree. Dead high e string just sounds awful and I donāt know how to avoid plucking it.
Reading the comments here I am perhaps one of the fortunate ones that the mini barre A has not caused too much trouble (not always the case believe me).
That said Iām struggling to get any context from the lesson or trying it in songs where I can see it would be advantageous to use it. Having learned the anchor finger method in the early lessons it seems any change involving D or E wouldnāt benefit much.
@Richard_close2u can you suggest where this might be useful in future?
Hey @myall_blues, there are some answers to your question higher up in the thread.
Reading through it again, I find it curious that Justin says he doesnāt like the sound of the 1-finger A chord with the high-e string ringing. But, isnāt that just a normal A chord x02220? He seems not to like it when using 1 finger, but when using 3 fingers itās ok? That seems pretty odd.
@jjw the 3 finger A is usually used on acoustic when strumming the mini barre A is usually used on an electric with distortion and is used more like a power chord.
That makes sense, thanks. This probably also answers those who complained about not liking the sound of the muted e string. On electric that muted string is probably not even audible.
So if we are doing it with the first finger (mini-barre) it sounds better without the thin E string, but when played the first way we were taught, we do play it. Iām not sure I understand why.
Hi there, itās useful when you want to extend the chord and play with some embellishments where you play extra notes using 2 3 and 4th fingers around. So you can play A with barre, apply Asus4 with second finger and extend with pinky to 5th fret on B string or even jump down to low e string. Also helps when you move across the fretboard and use the shape as a triad and convert it to other relevant chord depending where on fretboard you are. Hopefully it makes sense 
Bart not sure what guitar you play but if you play it clean - no difference whatsoever for beginnerās ear and slight difference for those more advanced IMO. If you have an electric ramp up your gain and distortion and see which one sounds better I personally hate when open e string rings out on gain makes it sound like it doesnāt fit there.
I see your point, thanks. Iām lucky to have both an electric and acoustic, but I donāt have a single pedal (other than a tuner) and donāt think I will any time soon. One day Iāll be good enough and wish I could do something specific and that will be the day Iāll wish for some type of pedal or other. For now, clean and some crunch from my amp is plenty. I have a better listen but I enjoy the complexity and richness of more stringsābut I may just need to develop my ears a bit more.