I dont know.
3 teams come down, they bring with them the promise of 4 years worth of cash to spend in the CC and League 1 (usually) - so from the start some of that money is benefiting other League teams
Secondly, and someone please feel free to correct me if Im wrong, but if a team goes up before the scheduled end of their parachute payments, the excess is wrapped up and given to the FL to distribute. So, assuming after 2 years all 3 of the relegated teams have gone back up, there there is (3x2) years worth of cash for the FL.... each season.