Well I can see in your avatar pic why youd want to. but I dont have mine at the bottom. They are actually very close to the surface, just facing at the front glass pointing downward. Two Tunzes are placed this way and one koralia is on the left glass pane near the back panel. Again pointed downward, it keeps behind my rock wall completely settle-free. I figured building upwards as much as possible is best cuz I like the look of the Coralline encrusted open bottom. So I get plenty of LR surface area in there as well as open space at the floor.
Also IMO you really dont want lateral flow like you might get with a floor skimming Vortech. Ive had better success ricocheting against glass on angles, colliding with other pump outputs to create a random flow. I used to do it the other way where I had the three pumps creating a whirlpool flow. This was the absolute best for BB maintanance as it all detritus would pile up in one neat pile. But once I switched to random, colliding flow scheme, the corals, rock and anenomes seemed to appreciate it more.
Of course if you have the vortechs rigged to some ultravariable, randomizing wavemaker, it would probably do the same thing.
One more thing, I also have two sub pumps in my sump returning water back to the MT. These also point down... straight down actually.
Acheive suspension in the best way for you and youll have a much easier time keeping a BB clean. Then all you might wanna do is periodic rock dusting. Youll be amazed how much crud will come out of those knooks n krannys in rock, even if youd done it a week or two earlier. Then again I feed a whole hell of alot. heh.
maybe experiment a lil before you drop the loot on the Vortechs. Those pumps, if affordable, will always be a nice thing to have though. GL mon.