Using the push-back from Secondary Button as opposed to the GSX pushback, which IMHO, is much more realistic, why is it that the FS2Crew push-back takes the aircraft so far back at a shallow angle that I'm almost into the jetways on the other side, as was at KIAD, whereas the GSX push-back is spot-on? Is there a way to integrate the GSX push-back into that Button Control menu, or would I be best just to bypass the FS2Crew Secondary Button's push-back request and opt for the GSX menu only?

Same problem here, I just use the FSX push back as the Video Marshall to remove chocks etc, causes to many dramas.

The FS2Crew pushback is wide because it uses the default FSX pushback system.  We can't control that.

 

It's one of the reasons we're making our own GSX style product (Ultimate Ground Crew X) to get around FSX limitations.