Rail gets here today! I will let you all know.Good point, the low rail may use reduced head height socket head screws or flatheads so they don't stick up above the rail, while the high rail might use regular full height head socket head screws since there's plenty of room for a deep counterbore. Much like button head screws, the reduced height head screws have lower max torque values than standard full height head socket cap screws.
I don't have my ATs anymore and even then I never had the high rail, so I don't know if the hardware was different. Earlier I was citing the page out of the 2015ish AT armorer's manual that only lists 3.0 Nm for the scope rail screws; no mention of high or low rail.