it would improve circulation if it was on the opposite side, but since the tank is a room divider and you don't want to see any plumbing i understand your reasoning. were you planning on drilling the tank for the return or going over the top of the tank? if your plan was to drill the return then you need to put it on the other side of the tank. you're already talking about 3 2inch holes (more or less depending on the size of your bulkhead) on the narrow side of the tank. you need to leave a few inches between each hole in order to maintain the structural integrity of the tank. as it is with three 2" holes you would have about 3" in between holes. I would consider this a bare minimum. before you proceed to drill i would get some additional opinions about whether or not this is advisable. if the return is going to be on the same side you will need to run it over the top of the tank and you will need a koralia or something on the other side of the tank to generate some movement.