The vanilla behavior of the armor perks Custom Fit, Well Fitted, and Matching Set is to count the number of heavy/light/material armor keywords present on the actor. Previous attempts to remove the helmet requirement would just reduce the number of keywords required from 4 (head, chest, hands, feet) to 3 (head, chest, hands or chest, hands, feet or head, hands, feet), so you could still get the bonus with a bare chest. In the case of Matching Set, the shield counted towards the total, too.
But because I just spent a few hours adding about 200 Specific Armor Keywords to all 2500+ armor item records in the game, it is now possible to make these perks specifically check for cuirass/gauntlets/boots keywords matching the type or material specified.
In truth, I just whipped this up to demonstrate what SAK makes possible.
Requires SAK: https://www.nexusmods.com/skyrim/mods/95387
Which requires USLEEP: https://www.nexusmods.com/skyrim/mods/71214
Which requires all DLC
Original URL: https://www.nexusmods.com/skyrim/mods/96011