I never lost a clown until recently when I moved my two Percs into a new 135g, I also added two misbars. 3 of them ganged up on the smallest, he ended up jumping. Then the two remaining percs ganged up on the last one. During that time, I had added two black false clowns, not realizing the issue. The smallest black clown jumped and that was it, I removed the last misbar. The last black clown is still in the tank, but holds his own against the male perc. All in all, from my experience, aggression lends to the jumping, if you see other fish cornering the clown high up in the tank, odds are your gonna find it on the floor. In my case, I couldn't revive them, had to trash them both. Up until this event, I would have never thought a clown to be a 'jumper' but it does happen.