Leaderboards will tell us how many players have a particular peen.

So (speculation) perhaps each peen will have some pool value, divided between each player who has it. Say pool1 = 40 peen points™, 4 players have that peen, so each get 10 peen points™. The maximum peen points™ any player has is 2000 (for all their peen) 10 / 2000 * 13 = 0.065, so having that peen will add 0.065”. If 5 players have that peen, it becomes 8 / 2000 * 13 = 0.055.

It might be the case that being in a particular pool gives you a minimum length increase, plus a pool bonus. That would be more difficult to calculate.