You can place the tank anywhere there is room for it but will your engine draw from that area?? This is one of the reasons I like pumped engines. I have had problems in the past with some planes due to lack of room for a tank, sort of like the plane I'm building right now. I had to place some items in the way of where the tank should go so it no longer fits. I had to place the tank way back under the wing saddle. Instead of fighting it and doing a lot of vodo crap like the last time this happened I switched engines, I went from an SK .91 two stroke to a 1.10 YS. YS engines are pumpers so it fixed the problem. I could place that tank under the stab if I wanted it.
I fixed the last one with almost the same problem by using a bleeder tank in the very small area just behind the fire wall, it worked out very well but took a lot of fooling around trying other things before I hit on the bleeder tank.