There are variables to this answer, so I accept no liability, and suggest you look at things closely. With my big tank the rim that is designed to hold the lid got in the way of my HOB's, I simply cut it to fit removing as little material as I could. In essence, the inside lip is there for the lid only and not for support of the tank, the center brace and the rim that goes over the glass are critical.
With aa 10g the only thing that should ever be in your way is the hood/lid, so placement on them is a matter of adjusting the back lip of the lid.
BTW: I don't know how other people cut Thermo-setting plastics but I use a small soldering Iron, with a new tip. It goes through plastic like butter, and leaves a rounded edge that won't catch or hurt anything.
As far as placement, if the filter will fit somewhere that I don't want it, I re-adjust my thinking. I am a circulation fanatic, so I have an RFUG in every tank right now. and I can put a heater and hob any where in the tank and get good circulation because of the RFUG flow. Without an RFUG, I would suggest placing things that create flow like you heater, hob, or powerhead the best you can figuring out flow is fairly simple, just feed some sinking granules right before a water ghange. watch where the granules go in the tank and you'll know if you have any significant dead spot. then vaccum them out immediatly so they don't cause other problems. Almost every thing in a tank affects flow in some way, and a little experimentation will allow you to figure things out.
