My Funtana used to tuck to the belly real bad in knife. It'd end up snapping out by the time you got enough correction on the elevator. Later on I had the wing dowels chew themselves out so I sleeved them with 10mm alloy tubing. When I opened out the holes in the bulkhead I filed away at the top of the hole only (towards the canopy). This gave about 1mm of extra wing incidence. It almost completely cured the tuck. I have 10% up elevator mixing with full rudder. One other thing I did was to reduce the rudder movement a bit. It was almost touching the elevators at full deflection before. Mine will hold a steady, no hight loss, knife for ever at half throttle now. Hope this helps you out.

Gez