I tried the Retro30/ET-65 X pattern and didn't like it. It seems that the speakers are fighting against each other. The ET-65 is a little overwhelmed by it's arrogant brother. I didn't like the ET-65. Too shy. It wasn't doing it's job. The sound emitted just seems messed up. Left vs right, up vs down.
I didn't suspect a major change running parallel with ET-65 on top.
But now the Cab runs almost like a single beast. The frequencies compliment each other. Running parallel is almost like have two distinct Cabs. The ET-65 just opens up and it's little brother on the bottom begs for attention.
My Cab isn't great. Ibanez Toneblaster, made with MDF. I cut open back middle third because it seemed very restricted.