Here I go jumping in with both feet again, will I ever learn
There is absolutely no point in asking for the P2P shield to be optimised if you don't state how it should be optimised, to serve what purpose, especially in its current form it does what it says on the tin, it will scan downloads of all p2p traffic for supported p2p applications.
Now if that p2p application splits a file into many, many packets and gets them from multiple locations, adding them to a single which is constantly modified than avast will rescan the modified file. That is a fact of life, the file has been changed, it needs to be rescanned.
If it isn't rescanned just because it is the same file name, this makes the whole point of having a p2p shield pointless, so you might as well switch it off if that is what you want avast to do. Of course you could always do that if you want already and have your p2p application have avast scan the completed download (if it has that functionality in the p2p application) using ashQuick.exe.
Now I really am done.