Position for road or TT matters a lot for the helmet.
Both seem to have helmet designs better suited for "head/eyes way up" or a more "head down" or a more "turtle" style riding position.
The other thing with this is sniffing out the differences you really need a good "protocol" and decent equipment. A wheel speed sensor, GOOD power meter, and a bit of Excel magic and formulas. You can't just ride the same ole loop back to back and say "I went faster" or it "sounds quieter".
I always assumed one helmet I owned was a good one for me in TT. Then found out despite it being one typically testing well on folks......was a bit of a dog.