If it can fit, it will manage it, think about it, you could aim yourself through a gap that you can fit through, it's no different. Sucks though, looks like you tried to jump proof your tank. As for damaging themselves on a hard surface (tank hood or whatever) has anyone tried something like streching a small hole net over the tank with a gap between that and the hood. Might help absorb the jump without damaging the fish. Just an idea, although admittadly a pain maintanence wise. Something to think about though if you have fish that you know spook or jump a lot.