Weird, I have a 406 on a 36 gallon bow, lots of flow, tons of surface movement, tank clears fast. Have trays packed with all the stock media, plus purigen and dish scrubbies. and I have a sponge prefilter!
I did try to use a lily pipe style outlet once, flow/movement dropped way off. Put the stock outlet back and saw immediate return to high flow (with mollies/platies nose into the current playing). Maybe these filters are not so tolerant of changes/additions to the outflow side