I did a bike fit with the LBS last year. Zero setback post on that bike. Change was made to swap out to a 70mm stem.

My new bike (exact same frame and geometry) has a 20 mm setback. The saddle was set up to be in the same relative position.

I can't quite tell if I should also change out the OEM 90 mm stem for another 70. It's fractions of an inch. Is a 20mm difference considered to be significant?