Tofer:
The question was different. What is more efficient for the project either to have 3S and one step-up module or 4S and a step-down buck?
Depends entirely on the efficiency of the specific converter and there are no general answer. If your input energy is supplied as (nominal)11.1V @ 4Ah or 16.8V @ 3A you still have the same 44.4Wh of energy.
Steve