In the link below, Emily Kwok shows a bow and arrow choke starting from a mounted position. The grip concept is the same from the back and she shows it from there as well. I know I’ve worked harder than necessary to finish gi chokes because I didn’t grip the collar correctly. Don’t waste your great positioning with a lousy grip:
https://www.youtube.com/watch?v=nS6ALx73epc
Lachlan Giles is always a good resource. This video covers both the Bow and Arrow Choke and the classic escape from the back:
I’ve often used a variation of this technique:
It feels like an escape, but it’s still death.