If it is too tight front to back, I suscpect you have the wrong shell shape for your skull shape - OR the helmet is just too small. I have a Large RX-7 Corsair and a Large Signet GT-R. The Corsair fits like it was custom made for me. The Signet is a little tight, but doesn't give me a headache.
I would suggest going to a dealer that stocks Arai and try several different sizes and models on to see which fits you best. When you find the one you need, go buy it online and save some $$$. I got both helmets on eBay, brand new, Corsair for $415 shipped and Signet for $260 shipped.