Well, after a few days break from the YH3s and YH100s, I put the YH3s back on the desk for more dampening adjustments. The ESW9 pads were really bothering me as they just didn't produce the bass I expected them too and I only had one theory why. So I made a ring about 1/4" wide to surround the driver opening on the front bezel, then stretched the ESW9 pads over that:

I had changed the dampening too and they were too under damped, so I added the disc of the synthetic, breathable felt to the drivers. Close but still underdamped. But great, deep bass! Pads were just friction fit at that point so I opened them up again and swapped in the Moorbrook felt. I stretched the pads over the cups for the pic above then listened. Damn. Too much dampening, but the shrill highs I had last time with the ESW9 pads were gone too. So now I need to swap back to the thin black synthetic felt and decide whether to try the fourth layer of cotton or add a second, smaller disc of the black synthetic felt in the center of the cup behind the driver.
Once I recable and get it dialed in again, I'll make ESW9 pads adapters for my YH3s and use acoustic caulk to attach them to the YH3s. Then I'll add the felt ring to the adapter opening to fill the ESW9 pads. And then I think I'll have the YH3s maxed out.
Which leaves the YH100s to adapt to the dampening of the YH3s.
But the YH100 driver is definitely larger than the YH3's driver:

I'm not sure if I'll take off all the tape or not. Might keep the center disc for now and dampen the vents with cotton batting instead of felt. I'll add the felt ring to the YH100 ESW9 pad adapters too and see how it sounds.