I’ve had Garrett Thomas’ Imagination Coins for a while and love the effect but have been nervous about performing this due to the angles needed for the R**s** s******y. It seems ok for one person but I feel that I might flash if fully or partly surrounded. Any advice or thoughts?

The angles are pretty good, especially when only hiding a quarter.
Check yourself in a mirror.
Also, you should just be briefly gesturing, not posing for inspection or freezing like a statue.

Thanks! Specifically, it’s asking the spectator to drop the imaginary coin into my hand that makes me nervous about the angles, as I feel as if all the heat is then on the hand with the coin in RS.

You do need to watch your side angles for that. That's a bit more like a Kaps subtlety, palm up, with the coin in FP vs classic, but it's still quite usable/workable.