The difficulty of getting a p2pool share is automatically adjusted to keep one share being produced every ten seconds for all people using p2pool, in exactly the same way that the bitcoin difficulty is adjusted to keep blocks being generated at one every ten minutes.
Tell me if I understood it right. Is it so that if I add some more miners the share time will decrease, then the p2pool difficulty must increase to reach the ten seconds again and therefore the weight of the new shares has also to increases for the payout?