Cervelo demonstrated how the geometry of many manufacturers frames move the headtube relative to the BB in a completely inconsistent way as frame sizes change.
Some frames have the reach actually increasing as you get into small sizes and stack reduces.
Check Specialized vs. Cervelo geo which is why Mark Cavendish can switch from 52cm to 49cm Venge frames and probably not even change his stem.
Cervelo demonstrated how the geometry of many manufacturers frames move the headtube relative to the BB in a completely inconsistent way as frame sizes change.
Some frames have the reach actually increasing as you get into small sizes and stack reduces.
Check Specialized vs. Cervelo geo which is why Mark Cavendish can switch from 52cm to 49cm Venge frames and probably not even change his stem.