Make sure you are hitting them with the robot BEFORE your MB F3 connects. It's does 43% if you hit them with the robot, then MB F3, and it only does 30% if you hit them with a MB F3 then the robot. Don't know why scaling acts like that depending on which move hits first.
EDIT: I just noticed that droid by itself does 18.00% no matter how many times I do it, however if you activate the droid, and do a MB F3 or MB B3, even if you dash cancel the MB, the droid will do 27.00%. That's a pretty huge difference. I don't play batman, so does that work with all interactions, or is this some stage specific tech?