Bud, whatever 12ga model you shoot best is what you should replicate in 20 ga. The stock drop at heel and comb varies brand to brand, the grip radius, the rib varies; low, stepped, high, etc. Do you pattern your 12 gauges? Are they centered R/L? 60/40 55/45 % high/low?
I was ”raised on Remington”…1100, 870, 11-87 had 14” lop, 2.5” drop at heel, 1.5” drop at comb. Modern shimming helps me replicate the “B” guns to my instinctive/conditioned pointing. The Beretta A300/A400 adjust well for me. They are available in 20ga, however have a forward safety. Browning Maxus II works for me with #3 shim. But not available in 20ga.
To the SX4 and new style M2 20ga…I Bought Both, could not hit with either! Tried shims(none come with SX4) and both guns patterned significantly High/left, 80/20, even after my attempts to adjust them. SOLD THEM BOTH. Handled nice, cycled fine, felt good in hand, But…