Nah its filled with fat not waterThe hump in all cichlids, is a water filled sack often temporarily based on alpha status in a group, so genetics is a very important basic factor. If the genes are there to make the sack large, it will be large, if not, thats the profile you get.
It is interesting that in lab experiments, females often don't choose the male with the biggest hump, out of a group, so that is probably not the only determining factor.