What I’ve found is, the “bigger head” combos are fussier about how they interact with the converter than a smaller head combo.
Especially when there are some compromises made to the engine combo for street duty.

It’s sort of like..... big heads, without the big compression and big cam, have a smaller tuning window at the starting line.
It’s just easier to make them work when it’s 14:1 and 280@.050...... you start with a 5800 8” unit and go from there.