IOW, if you tighten the cable to get the front cage to move far enuf to the right not to rub, it won't then release far enuf left to drop onto the small chainring? Yeah, that sounds like the barcon doesn't "throw" far enough (weird, since it probably rotates on its pivot pretty close to 180 degrees, right?).

One dicey option is to put the cable on the other "side" of the pinch screw on the derailleur. This would put it closer to the fulcrum, and make it throw the cage further for every degree the lever is pulled/pushed.

Possible caveats:
* This increases the effort the lever must endure as it pulls the cage to the right, and may eventually bend/break the lever, or snap the cable
* Since you have more cage movement per degree of lever movement, fine adjustments will be more difficult

I take it you've ruled out things like min/max adjustment on the cage, right?