16th note patterns are not supported by the Strumming Machine yet, AFAIK.
Sadly, I don’t think Justin focuses on 16th note strumming patterns in the beginner grades. I remember having to work out some of the techniques myself for songs like Wish You Were Here.
In a nutshell, you want to start with 8th note strumming…down strums on all the down and upbeats.
Then add in the 16ths as upstrums.
This post of mine talks about the 8th note strumming aspect, which might get you started.