I see what you mean QAVION the AMM and the schematics are not very good so it's back to the training notes and mine state
the right FCU will provide the signal to HYDIM system 1 card to turn on the pump (demand) for hyd. sys.1 whenever the flap control lever is repositioned and until the flaps are in agreement with the flap handle .The left FCU will do the same for sys 4.
So I would guess the answer to you original Q must be the flap handle RVDT
and the PFM
in the FCU.