Going to need first what the ref is for.
There's different setups (lighting, substrate size, flow) for different proposes; vegetation, amphipods, copepod, time out for fish, etc. Depending on the use, might make more sense just to be incorporating into the sump. If for pods, slightly higher than tank seems more ideal though pump shear maybe overstated.
Days worth of reading here
http://www.wetwebmedia.com/refugium.htm