Using Animation Layer to define body Type ,using multiple animations, one for body type and one for pose

Hey there, I am working on a Project where I am dressing characters using separated Mesh, Armature, and More Meshes to define a character as a Character Model, Armature, and Clothing.

I wanted to Create More types of Characters like Trolls, Dwarves, Humans, Who have size Dis-Similarities. So my plan was to create animation to define the Body scaling, exclusively for the clothing to work on all of the different body types. BUT when I use the Animation Controller the Additive layering does not seem to be able to achieve this. since all tutorials I can find on youtube Starts out by saying " We use Masks to separate arm animations from legs" or other sentences like it.

I know animations are a long list of Vector instructions for Every frame, and I wish to do a simple Vector + Vector operation here. I think i need to do it inside the animation Controller Overrider since that's how tutorials tell me I need to switch out animations. But how? does anyone know? then I would be grateful for some tips.

Also I haven't been working in unity for a long time so if you could be very clear, I would greatly appreciate it ,Hey I'm am working on a project where there is different characters using different clothing such, as well as being animated as one would expect.

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in this project i want to use the same clothing for different base character models. such as a human and a Troll, or Dwarf, or Whatever. Now I Thought I would be doing this using Animation Layers in the AnimatorController. However when I try to load in the "Body Size Pose Animation" and layer an Actual animation on top with additive layering, it does not in fact add the animations on top of each other.

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Now I Know that animations are vector data, stored for each frame, either keyframed or interpolated from such, and I am genuinely confused to why it does not work. Does anyone know anything about this?