RE: TH .46 ran fine upright, not side-mounted!
I think one part of the problem is the prop, it's a bit much. Try an APC 12X4, you should get 12K plus for good response. This is a narrow prop and I have good results with this one on a MDS .48 and Magnum XLS .46. Usually, side mounting will not give you any problems in the carb/tank position relationship compared to upright mounting. The biggest difference in moving the engine from the trainer to the Funtana would be the prop, I am guessing.
Try different props to see what happens.