RE: WACO YMF
The problem is that the Pica YMF (and just about everyone elses) is based on the original drawings by Paul Matt and he drew the airfoil as a Clark Y, but referenced the flat of the airfoil as 0 degrees incidence, which makes it very close to +1.75. He also states the rigging incidence as + or - 1/2 degree. The horizontal stab was adjustable +3 to -4 degrees. Pica's setting of +2 would put the wings flying very close to -.25 degrees. I was not happy with the amount of up elevator I had to carry on mine to get a good scale flying speed, so on the one I am designing and building now, I am making it adjustable.
If one looks at most of the pictures of the real ones, they are flying with positive incidence on the horizontal stab, so I suspect that this provides the most efficient attitude.
Les