Good Question! I have two #4's in my 93, and I can't seem to find a good solution.
Playing around with the position hasn't worked out. Pointed at the surface, great turbulence but not enough movement on the bottom. Pointed them towards the glass, pulls up all the sand, and sand storm ensues Pointed them toward the rocks, corals get slammed. At a loss, guessing that's why people get controllable units, atleast one of the reasons for getting a controllable units.
I was going to place 3rd powerhead with much less flow near the bottom, something like a tunze 625 or seio 620.
If you purchase a timer or controller to use with your 4's, I'd be interested feedback. Good luck with it.