[Loadouts: Low Tech] General Guidelines for Thigh Armor Penalizing DX?

I really like the realistic flavor of the optional rule in Loadouts: LT, pg. 4 that gives a -1 to DX for "any heavy or bulky armor covers the thighs". My problem is that the guidelines given in the rule are very general and the rule itself seems to be applied inconsistently throughout the supplement. For instance, the heavy mail Halysidoton in the Byzantine Cataphract loadout covers the thighs but no penalty to DX is listed, while similar armor on the Huscarl and Norman Milite give a DX penalty. Likewise, the Heavy Leather Buff Coat on the 17th Century Harquebusier, which covers the thighs, gives no penalty to DX despite the great weight of heavy leather armor.

I know the rules need to be general because of the nature of GURPS and that there are word count restrictions when rwriting GURPS supplement, so I get that the rules could not take into account every case and type of armor. However, I am just wondering if anyone with more knowledge and experience with armor could give some more specific guidelines as to when the rule should probably apply, or at least flesh out what principles one should consider when trying to determine if a thigh armor type is "heavy or bulky"? I would have expected the heavy leather of a buff coat to qualify as both heavy (20 lbs for torso) and bulky (not flexible per LT), but I would seem to be mistaken.

Beyond general principles I am also specifically wondering about fine mail and the medium and heavy levels of layered cloth armor. Do some or all of these qualify for a DX penalty? Does it matter if they are leggings versus skirt-type armor (especially hanging from torso armor)?

Thanks!

[Loadouts: Low Tech] General Guidelines for Thigh Armor Penalizing DX?