I am concerned about the BB/eccentric ability to provide enough tension too. The shop we bought this frame from insisted it is "Gates compatible" and that Calfee has been building them to a standard bottom tube length required for the Gates belt drive. Since the eccentric is already currently in the 4.5 o'clock position and we are just getting 28.5" at that position, I agree with your observation. I think our bottom tube center-center of the BBs measures 72cm, which logically matches the stoker top tube length given our frame has identical 74 degree seat tubes for the stoker & captain. Based on that, I think we are maybe a 1/2 cm short of the optimal bottom tube length. But doesn't Calfee build most all their current frames with a 72cm stoker top tube and same seat angles?

I'm picking up a ball-end hex tool tomorrow to fit into the eccentric bolt heads with the BBs installed - the design of this particular eccentric makes for a very limited tool fit.