Quoted from zacaj:
Each time you hit any targets the bank resets, yeah. What do you mean about the number of hits changing? I never really pay attention to the amount of hits, just bash the bank a few times and I always get it. No add-a-ball in tie fighter besides from maybe via the random pop awards? Hyperspace sorta has its own add a ball though I haven't figured out the rules to it yet...
I guess your original post stated once you completed the drop targets it would light the add a ball, technically that wasnt accurate since they reset immediately once hit and all you have to do is hit any drop target enough times.
My comment regarding the number of hits differing between planet multiballs was just that - some planet multiballs only require a few hits to the drop targets to light the add a ball, where as others like Battle Above Endor requires what seems like twice as many hits to the drop targets to light the add a ball.
Fun fact though, if you dont use your add a ball button during a planet multiball but start hyperspace multiball after you can use the button to add a ball during hyperspace mb.