[Plane]

We can entirely avoid the question of where the knee begins/ends by focusing on the armor aspect, which is really my central concern here, whether or not you have some versatility in striking surface if you had limited protection.

Firstly, we know there is a move called the "Shin Kick" which gets +1 damage when wearing rigid leg armor.

I posit we slang-term a "Greave Kick" because if you are wearing a greave on your shin, you're actually connecting with the greave instead of the shin. It's an alternate name to help distinguish the unique factors (+1 to damage, and DR protecting the shin).

Based on that, I will invent these names based on my idea of "Knee Strike" variations that connect with different pieces of worn armor:

"Cuisse Strike" (thigh below)
"Poleyn Strike" (knee below)
"Greave Strike" (shin below)

Also wondering what kind of variability exists with the kicking technique. Feet is the most basic, MA clarified shin... apparently you can even do a knee attack with it using the kicking rules, so thighs (cuisse) are the only non-addressed portion of the leg I guess.