Interesting, what kind of bridge do you have?
Synner Official Website
Try to watch the Lesson on it again. Get a small Pick that forces you to Focus on technique (eg a Jazz III) and Play something you are comfortable with playing. Just have fun and don't get frustrated and don't overthink it. Eventually you'll get there. That's what helped me.
Knuckles under techniques are not for everybody. I can't even get my hand to work that way. I hold the pick like a key for a door, and my other fingers fan out. If I tried to curl my knuckles under I wouldn't even be able to get the pick to touch the strings. What works for Syn and Papa is not what works for everyone; Papa says as much in the video - there are as many ways to hold a pick as there are players.