I'm sure they will take the command bridge into account. If a Year 12 FO from BA became a captain they would join Year 12 captains pay scale. If a yr 12 or 13,14,15 year FO from bmi became a captain they would join year 1 captain pay scale.
With this in mind most FO's will do better joining the bottom of the list. I think it's down to the pension!