The tailplanes angle is only related to the wing chord line. The fuselage is there to maintain this angular difference. For all 'normal' models this angular difference will prescribe the 'S&L' speed of the model. If you set the tailplane chord line at 1 or 2 degrees negative to the wing chord line you will find that, with a 30% balance, the model will be speed (pitch) stable. The model will not 'rear up' at takeoff, unless you, the pilot, have done something grossly wrong, the model is grossly overpowered, and the wing/tail diference is way too much. The balance position is chosen for the degree of pitch stability you want, the old timers with large tailplane areas can simply stand a greater latitude in balance position the more modern designs without getting into an unstable region. As for the 'flap' action of an 'undercambered' airfoil, it's not something I have ever noticed, and I have flown these sections on all sorts, from gliders to scale models of very early (1910) airplanes. There is a huge drag rise with increasing airspeed, and a tendancy to climb, but usually fuselage level, not noticeably nose up. Provided you fly the model with a reasonable degree of intelligence, the wing loading is not excessive, the balance is conservative and power is reasonable you will have very little to worry about.
Evan, WB #12.