Somewhere in here is Gordon Delany's recommendation for improving the Pathfinder profile. I scratch built one like he said and it flys a lot better than the kit version.
Gordan's usual build tips/mods are:
1. Set the hinge to hinge measurement at 16"
(this may require cutting a bit off of the end of the supplied Brodak fuselage)2. Build the stab and elevator from 3/8" material.
3. Sand a mild taper into the tips of the stab and elevator
4. Keep it light.
5. Build it straight.
Also, I would recommend that you laminate two 4x36 x 1/4" pieces using 30min epoxy for the fuselage. Much stiffer than a single 1/2" plank.