A while ago during a tough melee fight I accidentally touched ctrl (i've set it as toggle) and crouched in sneak mode. My opponents suddenly missed a lot more.
I thought it was just a coincidence but have used it more frequently and do have the feeling avoiding to get hit is easier in both ranged (archers) & melee fights when sneaking .
I do use https://www.nexusmods.com/morrowind/mods/43108 which changes i1stPersonSneakDelta from 10 to 25 .
Uesp wiki & openmw wiki/research don't mention sneak as changing hit/to-get-hit chances.
Maybe a crouching character has a smaller hit box and is therefore harder to hit ?