IMO, the 20 and 28 gauges need tighter chokes to perform on the par of the 12. Your success with the 28 is not surprising as witness the averages on the skeet field in the NSSA. It's without a doubt my favorite gauge to shoot, followed by the 20.
Screw some tighter chokes in that Citori and watch what happens.
If we ever meet at a shoot maybe we can put together a 28 squad and have some real fun.