How is the mask(s) for Undershirts defined....?

[spacefiddle]

EDIT: SOLVED, MASK IS ALPHA OF NORMALMAP HARHAR

So, looking at, for example, the basegame "leather shirt" vs "Martial Artist Bindings,"

- Nothing I see in the FCS for these objects seems to point to a mask
- The Diffuse textures for these items have nothing in the Alpha channel that would be a mask
- Yet these two items not only replace different regions of the body wearing them, but they do NOT cover the entire skin - so they each have their own mask, somehow, somewhere
- Part map is not being used (except armpitslol)
- Nothing in the respective FCS entries (shirts, bindings) seems to point to or define a mask

How does the game not only pick a mask for these items, but picks two different masks?

Asking because I am trying to create a new object. I copied an existing Undershirt item as the base, but even tho I gave it its own Diffuse texture - and my new object points to it, in my mod directory, in the FCS - when a character wears it, the original base item's texture is what shows up, and of course, in the vanilla-masked locations.

How can I find the mask definition for my copy? Or create/define a new one?

Thanks!

Addendum: it cannot be the "skin body mask" defined in the race, because if you look at it, there are unmasked areas in the mask texture but the Bindings and Shirts show up on those areas just fine. So that ain't it.

[spacefiddle]

Maybe specifics would be more helpful:

I am trying to create Martial Artist bindings for Hivers. Looking at the unwrapped Hiver skin diffuse, I've made "cloth bandage" texture over their big ol' three-fingered hands, saved it as a new BC3 DDS, etc.

In the FCS, I duplicated the human male bindings "undershirt" object, but pointed my item to the new texture i just created. *But when my Hiver wears the item in-game the bindings appear in the same places as if I had allowed him to wear the Human-textured object!*

Which is bizarre, because again, i see no mask defined in the FCS that corresponds to the Human Male's wrists, back of hand, ankles and feet, stomach, etc. And the texture only appears in those areas - with no mask you would expect the entire skin to become "cloth wrapping texture" but it doesn't. So some kind of hidden mask "came with" the object when I copied it. Therefore I assume if i created a new FCS undershirt from scratch, i would in fact wind up with "cloth wrapping mummy man" if I pointed it to my texture (since whatever magic created the hands-feet-torso mask won't be in my new object). Still with me?

plz send halp

beep

[spacefiddle]

HAHAHA NEVER MIND FOUND IT IT'S THE ALPHA CHANNEL IN THE GORRAM NORMAL MAP

leaving this up for posterity in case anyone else needs to mess with "undershirt" items

[spacefiddle]

Update: crude test successful and now I can see all the areas I need to cover more clearly. Also I'm thinking I need to change the color of their wrappings - the basegame's bandage color just blends right into Hiver skin lol.