Perfect! So others have realised yamaha have messed up with the intake system. Good find mate.
I am not saying that it's impossible, but I have put around 200 hours in the sand between my 2011 and 2014 YZ450s and have yet to have any issue what so ever. In fact, if anything, the filter area remains cleaner than it ever did being under my seat. While the front entry air intake may seem like a bigger target for debris, your rear tire does far more damage to an air filter than your front ever could.
Choking up your intake with foam seems like a bad idea to me. Make sure you have a clean, well oiled filter and you will be fine.