Definitely two schools of thought on this. Some say put it on the bottom, some say elevate to maintain a small level of stratification and cooler bottom water.

While I'm sure having the diffuser on the bottom will definitely stir up more silt, with time I think that decaying matter will still be handled. Just takes longer.

As long as water can circulate downward to the bottom, O2 is still being introduced, maybe not as heavily as a bottom set, but it still gets down there.

I don't have a plate on my diffusers. They're mounted directly to the top crate, so water should be pulled up from below/thru the platform. It's just not causing a major disturbance of the bottom. I still see a little silt, but only on initial start-up then it clears up.

.10 surface acre pond, 10.5 foot deep. SW LA. The epitome of a mutt pond. BG, LMB, GSF, RES, BH, Warmouth, Longear Sunfish, Gambusia,Mud Minnows, Crappie, and now shiners!!...I subscribe!!