It doesn't even touch my head (or helmet). I actually forget that I am wearing it, air flows through it quite well on the track. It is mostly made of a perforated fabric instead of being a stretchy, skin tight material. During the hotter months, I don't even bother to wear a jersey over it. When I come off of the track on a hot day, I just pull it off.
Also, if you have (or are considering) the Leatt, I can see no reason that the EVS wouldn't be compatible. You would put the brace on and zip the armor up over it. Putting on your jersey will be a different story.