SG, if you're using the same powder, the same amount of powder, and the wad is seated against the powder, then you have the same area for initial gas expansion. I don't care if you put a 5 inch wad in front of it, it makes no difference. The wad weighing a little more figures in the formula along with the shot when calculating recoil but that's about it.
Alliant publishes two 7/8oz. loads, consecutively on the page, using two different wads.... the AA12SL with a 20ga. card in the shotcup and the AA12L.
The sole difference is the length of the crush section.
The pressure difference is 600psi, which for this load is 8.3%.
There's a difference, if you think so or not.
