I dont use any magic math, i have atv-wedges and R11-irons use cally lvl33-balls, grenside bunkers all depend on how high are you down below greenside, exampæe hole 15bpb, left frontbunker is very low, but not deep only 20% from that i add 5-10, depending on wind and use a full short, works great, to get the backroll from behind the pin..
WEll in more plain bunkers, to green , but deeper 40% i add 10yds with a full or if its possible to get on within 1/3 of distance i pitch and add 5! The deeper on oly f.ex 50-60% or 40-50% i add even more and use a full, 50% i add 20 and 60% 25, and gets very close almost every time!!
I dont know the distances on your wedges, but use avatarmoves, there are 11 from 0 to full, what means each move is 10% the 1. move is just to set club in position to shot!