What works for me beyond using any formula...
Map the club & ball used with every bunker situation. I use 100%, 98%, 95%, 92%, 90% and so on. Include moving the spin dot below the sand & just above the sand.
Also note the distance carried. Bunker depth & fridge length as these will impact the required percentage needed.
Map bunker shots with the flop shot. With flop shots aim about 1 grid left.
Map fairway bunker shots.
Know that varying green speeds, elevations, etc may alter the mapped shot.
For fun, practice hitting out of St. George bunkers.