Could be. But I'm still intrigued. If the inner ring is close enough to the chainstay that you think a shorter spindle would make it hit the stay, you're fine with the BB. Assuming your triple FD has a straight cage front to back and top to bottom, it's not the FD- especially since you have a friction DT shifter up front. And I've never seen a case where even extreme cross chaining will actually cause a big ring shift. So, three things remain:
* How close to the big ring does the FD cage sit? Should be about the thickness of a nickel as the cage passes over the teeth on the LARGE LOBE of the BioPace ring (there will be more space when the small lobe is under the cage
* Is the large ring installed properly on the crank arm? There's a small shaft attached to the outside of thebig ring and it should be placed UNDER and toward the crank arm. The middle and small rings have a 'V' stamped into them, the V should be installed so it's in the same orientation as the shaft on the big ring, but facing inward
* Is the large ring so worn out that the short/shar toothed teeth simply can't keep it on the ring?

BTW, pics might help.