As far as I know, the mail loop is a modern convenience so that you can put a belt directly through it; I've only seen it on the IceFalcon ones (though I haven't shopped for any for years). I bought the IceFalcon set, didn't like the wonky loop, cut the tops down to approximately "cuisse" sizing, and added a wide leather tab to suspend them with.
I do remember seeing/hearing about crusader era wearing the padded chausses over the maille, instead of under, though I don't understand why.
Nathan made what he called "cheater chausses" the same way (just the knees down); he might have more info.