FYI,
If you want to wear your aero helmet and a backpack - the tail of the helmet and the backpack don’t play well together…makes it very hard to lift or turn your head which can be a problem when you are riding and trying to look around…
Dave
agreed…I hope that you found this out the way I did trying to ride the bike to the transition area with the rest of the stuff on your back and not trying to be the dorkiest commuter ever 
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I have seen several people wearing their helmet backwards when leaving race for the same reason. Not going to offer the best protection, though. But then I have observed people racing with the point in front, too. My Giro doesn’t fit well backwards.