Test glides of a model of this size from arm height often do not show up marginal problems. But it's a positive thing that it didn't try to tuck or flip up right away. You may still be in for a handfull later but at least you're in the ball park.

From the original pic I'd say that a decent starting point for the conventional mode balance point would be at the 50% root chord point. The swept wings give you that much at least.

Something to keep in mind on models of 40 to 60 size and wing chords of 10 to 12 inches is that a CG shift of 1/2 inch is considered big. A shift of 2 inches is a disaster waiting to happen. I offer this last bit because I'm not sure if you understand the scope of what a CG shift can be without going WAY outside of the acceptable parameters.