I know the play is limited in our crossbars due to the heim joints, but the bar really needs to be pulled from the throttle cable attachment, all things considered. Especially true for people that have slop in the linkage.
I like what Danny says (again). All of us are surely converted to heim-joint linkages by now, but one must also consider that the hex-bar has "torque flex" from one end to the other; enough to make a quite noticeable sync variable.
For example, pull off idle very slightly on one side's carb actuating horn and you'll notice the engine shake as the carbs don't come on in sync. The other side's carb is pulling in late because of torque twist in the hex-bar. On the other hand, pull from the throttle cable and the sync is smooth (presuming the sync was performed with the cable or its attachment point).
Also, I like to make my first sync adjustment at just barely off-idle. That is when you can tell if one carb is trailing the other. Then go to 2000-3000. If not sync'd there, then maybe some linkage geometry issues are at play.