I don't think the tank is the problem. The tank being to high or low means nothing when the nose is straight up. If you are stuck using the short prop, so be it. I think part of your problem is over heating. Mostly because during a hover you are not getting a lot of air flow. I have a profile running a Saito 1.25 that will get hot during extended hovering. I stood next to Jim Flanigan last year hovering a DA-150 powered Yak. After 60 seconds of hovering you could smell the engine getting hot. It's the nature of hovering. Second thing to try would be a Cline regulator. This would keep a little better pressure on the tank. Part of the problem with a 8" pitch prop is the engine speed to hover will be lower than using say a 4" pitch prop. This is cutting back on how much pressure you are getting in the tank. Again adding to the lean/overheat problem.

David