I agree with DaveSSS. What C4L went into is not what I asked. Dave is correct in that adjusting setback to compensate for STA does not affect reach BECAUSE BB and saddle location should be the fixed points. Once the reach is known the STA is irrelevant as a component of that dimension. STA comes into play to select a saddle and seatpost that can put the rider in the right place with setback, rail length, etc. I scanned the Cervelo frame sizing presentation, didn't study it, and did like what I saw. The proportional increase in stack and reach makes sense to me.