>>1895723
I can execute it on characters as small as Froppy and as large as AfO, but I might be pulling it off in a slightly different way than you.
Explicitly following your directions, I couldn't land it on anyone. It turns out the most reliable way to do the combo is to melee the enemy, then take a step back and beta to the side of them, to your right. This causes you to catch them with the left side of your beta, which for some reason registers differently than a direct hit, and lets you alpha earlier to continue the combo.