Fork rake and fork offset are the same thing, so I did take that into account. The offset, as I understand it, is specified along a line perpendicular to the steering axis and not along the wheelbase. I wondered about the distance from center to edges of tubes, but I think the specs should take that into account (I could be wrong).

I think that the number of significant digits in each specification is probably the limiting factor, as the calculated result can only be as accurate as the input. In the case of my calculation above with the Vaya, I really should have given my answer as 660mm because I had nothing that would give me 5 good digits. Salsa may have actually measured to get their value.

If you're getting wildly different answers trying to reproduce my results above, it's probably a matter of degrees/radians disagreement in the sine functions.