its cool that someone else had the same general idea our team had btu took it a different direction, and its a nice finished product, though it feels a little shallow, since the only trade off is hitbox vs damage/bullet speed it meant that early its was a no brainer but to go with big since bullets were easy to dodge, but later there's so many enemies in such quantity you basically have to go small to survive but the fact that when small damage is decreased means you cant actually kill enough enemies to lesson the pressure(also reduced bullet speed makes you feel SUPER week when small, bullets are bullets and bullets travel FAST).
the above combined with the directionality of the U.F.O enemies made it feel meh in the late game since the best strategy to survive is simply to shrink to as small as possible, hope enemies miss and deal with enemies directly around you switching sides every so often.
still an interesting direction to take size changing space battles.
P.S. also i suspect you could export it as an html so its playable in browser based on the complexity which would likely result in more people trying it due to ease of access.