Fit question

I was just thinking about fit and started wondering, since the advent of reversible seat post head thingies (cervelo, kestrel, etc) If a bike fits you at a 75 degrees would it still be the ideal bike for you at 78 degrees? If the frame is still the right size what stem changes would you have to make ie. shorter, angled down more, etc.

More of a bike design question, what is it about frames like the cervelo which make it stable at both riding angles while others end up with too much weight up front…

Would a reasonable solution to having too much weight up front be a fork with more rake?

Just some thoughts