when you say you usually position seats back anyway, could it be that like in my case, it was just a bit too far back?

the one that had the weird "crease" rubbing was then on my dropbar bike, a Specialized Tricross with maybe 2 1/2 inches of seat to bar drop. After I resolved the rubbing issue on the right side, I ended up taking it off and putting it onto my mtn bike/commuter because I found the used one. I put the used B17 onto the Tricross and because of the lower handlebar position, I have it more level than the B17 on the mtn bike that has maybe 1 inch of seat/bar drop. Im the same weight as you.

Hope you can get it sorted, if not, its just a bike seat, you can sell it (and I'd be interested!)