The tube with a Fluval pre-filter sponge on goes pretty much all the way down to the gravel of my 10g tank. I can't think of a way to shorten it though since it has a larger opening on the end that fits with the upper portion. Is there a way to shorten it?
You could try cutting and crazy gluing it back together, or if you are running a sponge anyway, why not chop off the tapered strainer section of the tube, from what I can remember of the AC70 that should buy you at least 1.5"
Hacksaw to the length you want
Hacksaw slots halfway through the tube along the bottom inch (for water flow along the side, not just the bottom of the tube)
Fluval edge sponge over the tube, covering the slots
Tiny zip tie the top of sponge (not real tight, just snug)