[not mike s. but] If ponder has one pump and 4 trays total, stacking 4 trays high in a single stack would give greater velicity than 2 stacks of 2. Of course this is not how it was worded in this thread, but I think that was the intent of the post.
Running a heavier flow you have less buildup in the shower. At least that is how it has worked in my ponds, with LR, BioBalls, and K1, all of which stay clean for extended periods of time in my ponds, even without FIRs.