Hal,
I am having this same problem with my DP Edge. I too thought that the stab needed some positive incidence. However, when I added a little positive incidence, the plane dove down towards the ground at higher speeds.
I was thinking that I should add some upthrust to the engine to compensate for this. I already have 1 degree of UPTHRUST in the engine. Should I add more upthrust to compensate for the positive incidence in the tail? Thanks.