I'm with BigJimP, I might use 23 yards (Station to Center Post is 21 yards, because I got slow hands[Skeet]). I would also do all my testing (patterning) with the "Under" Barrel (just me). For trap, Under Barrel, Full choke at 35 yards & 41 yards, then use the Mod & Imp Mod when shooting Trap. Save the Full Choke in till you shoot from the parking lot (27 yard line)...
Have fun!!