It probably doesn't make much sense to direct the canister output down under the UGF plates. The water will already be pretty low in oxygen, so you're not going to be helping out biofiltration in the gravel bed much. If you just wanted to diffuse the output, going under the UGF plates would be OK, but there are probably easier ways (e.g., connect the output to a length of hose or rigid tube along one wall of the tank, with lots of holes drilled at various angles).
I have an Eheim 2215 that I feed into a spraybar that's about 3' long, and there is very little current from it... the water dribbles out.
Jim