I have not yet implemented the option to represent an eccentric BB. My excuse for that thus far has been that in order to achieve the required chain tension, the BB spindle could end up in any location along the circular path offset from the center of the BB shell. The average of all these positions is simply the centre of the BB shell. Therefore, although the BB spindle will never actually be situated there, it seems reasonable to design the bike as if that's where the cranks will be. However, I can also appreciate that it would be nice to be able to illustrate the differences in effective seat angle when the crank spindle is all the way forward as opposed to all the way backward as well as showing what you might call the effective BB drop when the crank spindle is at the top of the arc as opposed to the bottom of the arc. For these reasons and just for the sake of accuracy, I will try to implement that option in the future.

As for the seat stays attaching to the top tube, I had not noticed that issue which occurs when non-wishbone stays are connected to the top tube at an angle that is aligned with the angle of the top tube. I will have to correct that as well. Thanks for bringing that to my attention.