There are lots of misconceptions about how pumps should operate in the garden. Pumps operate in a cyclic way in the pond. When it supplies a waterfall a fair volume of water will be sucked out by the pump at one point and poured back into the pool from the waterfall at another. The widely held notion is that these points should be at the opposite ends of the pool.
This is completely wrong because current must be kept to the minimum. The splashing effect is good for the fish but if the current is too much it can affects the plants in the garden. Thus the shorter the distance between the exit and entry points, the better it will be in every way. So to make sure that the water movement is reduced, the pump must be positioned as close to the waterfall as possible.
Another wrong and impractical misconception which seems to be very popular is to have a fountain in a small upper pool supplied by water pumped from the main pool; the water from the fountain spray is supposed to overfill the top pool and then pour as a waterfall down into the main pool.
It won’t work; it can’t work because the volume of water that comes through a fountain jet is tiny compared with the volume needed to make even a modest waterfall. The water from the upper pool just wouldn’t pour, it would dribble.
If you really want this sort of effect it would be achieved by using two pumps, one small submersible siting in the upper pool producing a fountain, and a second siting in the lower pool piping enough water to the top pool to make a decent water fall.