The amount the share is worth is based on the target diff you were aiming for, not what diff the share ended up being.
Brilliant! Got it now thanks!
Uhm.
So what does the +d bit do at the end?
(No really! I'd like to be fairly sure I knew!)
+d changes the difficulty of work that is served to your miner. e.g., if you only want your miner to return 16 difficulty shares to your p2pool node, add +16 to user name. If you want your miner to tell the p2pool node to only send 5000 difficulty blocks back to the p2pool network, then add /5000 to user name. If you want both, append /5000+16 to the name.