It's pretty tough to get the original mechanism to register properly (not too much, not too little).
There is a splat sound when you hit him, and a bright flash.
I always full plunge and go for a skill shot down below that starts a mode for this very reason. Even if it is registering properly, it's much nicer to start a mode on one shot (while you still have a ball save) in the right orbit, than to need to hit a half dozen+ dangerous shots to accomplish the same thing.