I asked Nick M about the bit of foam when we noticed it.
Nick said that the Pro-Target, EV2 and FTP all vent air out of a hole in the bottom of the action. What he thinks though is that with the hole being directly above the hamster post, if you use the FTP without a hamster people may have been reporting that they can feel an 'air leak'. So his theory is that the foam is there to cure that problem (people complaining about an air leak that's actually normal for the rifle).
Seems odd that it has an effect on performance, I'm struggling to understand why that is (not saying it's not true, I just don't understand why?).
I may remove the foam on mine then, but I'll do a before and after chrono check. If air is vented out on every shot, it's doesn't seem likely that it's there to protect from dust - Nick's theory about complaints of air leaks sounds more plausible.
But then again, who knows? - I'm still struggling to understand why AA decided to fit that huge chunk of metal under the stock and a floated barrel that isn't floated ?