Hey victoria,
I too have been trouble feeding.
1)As for fish knocking the cup over, i put a rock on top which prevents that. My problem is after i take the cup off, its fully extended and looks AMAZING, then my cleaner and fire shrimp come picking at the leftovers and makes it retract. I have to leave the cup on for like 3-4 hours now to make sure as little as possible is left to pick out of the polyps "mouths"
2)Mine has so many heads, its impossible to be sure every one is fed, i shoot ALOT of cyclopeeze in the cup over the course of about 30 minutes, making sure every section gets a good bath in it and hope that each gets some
3) as to spreading, mine is the same, it has NO room to expand on its rock either. Im not sure how they reproduce. I have tons of tiny new heads all over but i dont think they will spread to other rocks like xenias or zoos will. I think they actually spawn but im not sure, maybe some experts can chime in on that.
Last, do you know a good place to get a tank and stand local? im looking for a 180-240 reef but cant find a good one or price.