You can actually help the miners on your node. Right now, you are relying upon the node to determine the share difficulty it will accept. Standard p2pool code will base the difficulty on the combined hashing power at the node. When there is a great disparity (like yours), the smaller miners are subjected to a much greater variance. Sure, each share found is weighted higher, but the larger variance means the small miner might miss out on payments because they don't have any of the heavily weighted shares on the chain.
The solution is easy, and is something you can do to help.
P2Pool allows a miner to determine his own share difficulty. This will override the node's setting. You implement this by using a "/" at the end of your BTC address. For example, if you want the node to only accept shares from you above 100,000,000, then you would put the following as your username:
This way the other, smaller miners on your node aren't penalized. The node won't count your hash rate in the calculations of share difficulty. Now, the smaller miners will find more, less-weighted shares, and you will find the more heavily-weighted shares. Everyone wins.