The small Sukhoi has a reasonably wide CG range but once it gets to the aft edge of the wing tube the plane becomes rather "exciting" to fly. It sounds to me like the CH may be aft of the wing tube.

Tom's method of pulling a string along the center of the wing tube and marking the tips works just fine. If you happened to have a couple of roller stands laying about you could slide the wings off the tube just enough to set the tube on the roller stands. That would easily permit balancing on the center of the tube. A couple of folding saw howses with a half round of pvc pipe on top would work just as well.

I don't but the 2 degree deflection stuff at all but if that's what he says....