A curved seat might help though.
This reminded me that Stefano at Slyway wanted to avoid using a head rest at some point, possibly because he races in mountains and head rests add weight. He fabricated a wedge perhaps about 12" long to fit the seat at the shoulders that would push his head and shoulder more upright. Maybe a 2-3" thickness at the top. The material could be any flexible closed cell foam and could be bonded with 3M double side tape or Velcro. This will make interaction with any head rest you have different although you could extend a head rest shape upward to fill the gap created. I use shiny black closed cell packing foam from shipping boxes for lots of things. Easy to cut with a big bread knife.
