I had the same experience with the Small Pulse Adder and idle AFR. Small adjustments make a big difference.
I also believe you are correct that the voltage/Kpa table has an effect on rich decel. Are you primarily adjusting V/Kpa at the lower MAP/higher vacuum values that you hit on decel? If so, do you see/feel a transition spike going from decel to on throttle situations? Don't you think some of the rich decel issue has to be addressed in VE too?
I can see more tail-chasing if global changes are made to the V/Kpa table and on throttle AFR gets lean too.