I've found this lesson to be very difficult, particularly because of the p rest strokes. Before this course, I was learning from Aaron Shearer's book, and he goes straight to free strokes with the thumb in his lessons. So it's taken a while to get this. More than a few times I wanted to throw my guitar out the window!
But I think I can now play them the way they're supposed to be done.
I'd like to just go through some of the issues I had in case it can help someone else. First, I started with my thumb too vertical. Almost straight compared to the strings. It was the only way I could get the nail to slide over the string. The problem with this though, was that it would most of the time not land on the next string, but would either hang in the air, or rest against my index finger.
Next, I tried lowering my thumb more like in the videos. Using the nails though, I needed way too much tension to get the thumb across the string. Also, the thumb would often hit two strings up from the string I was sounding, and then dampen the string I had just sounded.
In the next attempt, I tried not using the nail at all. I was able to sound the strings with less tension, but the sound was very muffled. I kept at it this way for about a week, not knowing what else to try. That started to get me frustrated because I could tell it was still wrong.
Finally, today I had the idea to rotate my hand so that the fingers were at more of an angle to the strings. And surprisingly, it worked! I can play with the thumbnail now, with minimal tension, and it sounds clear and unmuffled.
So really, do not give up. Experiment with how your hand is positioned, and just aim for a clear sound with minimal tension. Now the next step for me is to practice this over and over until it feels completely natural. It will probably take several months to get to that stage, though.
Here is a video
posting I found while searching for help. While it didn't teach me the actual techniques I needed specifically, it was good just to see it was
Now I'm off to practice and hopefully post some recordings soon. Hope this is helpful to someone.