Originally Posted by steelgtr
Does it get harder the bigger/heavier the plane is? I'm building a 39", 16 oz, FoamtanaS.
A lot has to do with how much vertical surface area is at the CG or even ahead of the CG for how well a plane will flat turn (or knife edge -- it's really the same phenomenon).
Unfortunately for you, the Funtana doesn't have too much side area up there. In general, the "prettier" they look, the worse they fly for KE. Conversely, look at the Tensor -- one of the best flat turners out there -- but ugly as sin. George Hicks did a great article in 3D flyer about what he calls SFG's, or Side Force Generators. Think of it like another wing in the vertical dimension. The bigger that wing is, the better you'll turn sideways (KE or flat turn).
Also, symmetry matters a lot to avoid roll coupling. Balancing the vertical surface areas on the front of the fuse above AND below the wing is a tricky thing for aesthetics, but makes trimming a whole lot better.
My Funtana 90 is pretty weak in the frontal area category, and suffers from poor KE and roll coupling. Some mixing took this out, but it took a few weeks to dial in all the variables. Maybe your mini Funtana has a slightly different layout.