I have a Fluval 304 sitting on the floor. the nozzle is about 5 feet above the floor. Its a PITA to prime, but with quick release, it rarely loses prime, so aside from setting it up the first time, I've never had a problem.
I think the manual says its benificial to have it as high up as you can.
... but who reads manuals, anyway.
"In this hobby - Bad things happen over night... The good things take time."
In Progress: 75 Gallon Planted Discus tank
Baby Sitting: 10 Gal Tank with single Convict