I'm assuming that you're using them as flaperons with the aileron and flap duties shared.

If so then you'll find that you can't use a lot of flap throw without creating a lot of adverse yaw. I built a 2 M glider a few years back and used flaperons as an experiment. Up to 10 or 15 degrees was not a problem but over that and the roll got lazy and the model was obviously fighting the aileron control. By 45 degrees the model basically ignored any aileron control and just yawed a lot. At about 60 the model was yawing and rolling opposite to the intended control. I only tried the full 90 at high altitude and the reversal was still in effect. So although I kept the flaperons I used them mainly for camber changing. I was using a very low camber airfoil so I had a little droop built in for extra camber and when I needed to scoot I'd bring them back up to 0 and the glider would move like a power model.

For a model like the Javelin, having just looked it up at the Bowman site, I'd say you're best off to use about +10 for camber changing but for coming down I'd go the other way and use them reflexed up a LOT like 60 degrees so they act as spoilers. That way the aileron control still works as intended. Use the full travel of the trim lever for the positive motion and then the real lever is available for quick action spoileron control with easy return to the previous trim.