Dick you really need to instrument the airplanes to really know what the changes you have made resulted in doing. Visual sight and trying to remember just isn't going to hack it.

What was a very experienced pilot doing flying in icing conditions. Good grief. You put ANY airfoil in the same conditions and it will come down It is an interesting story but has nothing to do with making a model airplane fly better based on sound engineering judgment and tests.

Nothing special about a flat airfoil. When put at an angle of attack it developes a flow field around it with a neutral point and the whole bit just like any airfoil section. They don't disobey any of the rules as we know them. There hasn't been a lot of engineering work on them since they are basically useless for full scale work.

The weight will effect the angle of attack you need to fly at but not the thickness. Symmetrical airfoils from 8-18 percent have pretty well much the same CLalpha curve, thin does have lower drag which does indeed provide for better penetration.