Free bump for a great helmet! (I've already replaced mine once.. that's enough for me for now)
But yes, the RSR2 and Race R and Race R Pro are different shapes for some reason. Whenever I tried on the RSR2 or RSX they wouldn't fit at all, but the Race R and Race R Pro fit perfectly. To consider, most of the people I know have heads too narrow/long (fore and aft) for the helmet. I'd say a medium round would describe it best.