I love the closed eyes! LOL, so cute.
The harness shouldn't chafe even when running, but some dogs are more sensitive than others.
Jackson has had his hair this short before -- so I would think you would notice. Part of it could be the way the hair swirls, as you say -- my guys are that way. When they are on their backs, if I sweep their chest hair one direction, they look like they have nekkid patches that move around depending on which way I sweep.
Keep this thread updated as to whether you see changes with continued use of your other harnesses.