I am looking for some guidance and help understanding what’s going on, please.

Long story...short.

I have set set up my recently acquired Mikkelsen so that the measurements match my 2 other bikes. However, it seems when I ride the Mikkelsen, it causes my lower back to hurt. How can this be, when the other don’t?

Measurements set equal:
1. Seat set back to pedal (when pedal is at full forward) and cranks are same length
2. Seat height from center of crank to same spot on seat (same seats, straight up through post)
3. Handlebars at same drop when compared to seat height
4. Handlebars same reach from seat (to bars and to hoods).

Am am I missing something?!? In my mind (which could be wrong) these bikes are set up nearly identical...but my back hurts on one and not the other two.

Help???