We're trying to get the fit on our tandem down, and are having real difficulty with my position on the rear of the tandem. The seatpost is a 270, and we (including our local shop) cannot find anything with enough setback. According to the shop, we have 20mm of setback on the post we have now (I'm not sure how to measure it). Anybody know of a seatpost that 1) comes in this size and 2) has more offset? My knees thank you

CA