Yes, Iron it would be very helpful if you could search for and find the tutorial topic I posted on making helmet fans to put into the helmet. Just use darkesword2020 as the search term, it should find it.
With all the outfits I have worn/made that incorporate fans(mascots mainly) the biggest headache was breathing the hot, stale air. The best placement for fans, that I have found, is where it allows a constant flow by the face and mouth, keeping the air fresh and the wearer happy(happier). Under the chin works, on the top of the head works well to, most of the outfits have it in that general area.
The fans are not loud enough to cause any problems when talking to people, so near the mouth would work well in a speaking role outfit. A great piece of headware to go between you and the helm is a buff. It is a nylon scarf thing that is one tube you can put on your head in many different ways. I use it personally when cycling and doing "hard hat" work but many people I know wear it under any hat that they might get hot in. It helps keep the sweat off your neck and keeps you cooler. Try it out or maybe just a bandana if the buff ain't your style. Great alternative to putting a fan behing your head.