Mapping one single texture to an entire Atlas instance?

Trying right now to overlay a "normal" texture onto an entire Atlas instance (not a TQT) and running into some odd coordinate issues.

What I want is to drape one standard/normal (non-TQT) texture over the entire Atlas instance - just like how the TQT image is draped over it. Thinking it was just a matter of what coordinate I used in the shader, I tried this...

float4 shadowColor  = tex2D(shadowMap,  IN.texCoord);

...since this is the same coordinate (IN.texCoord) used to pull out the image from the TQT image. Unfortunatley, I get something like this...

So I went into AtlasInstance::renderObject where the shader is set up, and noticed that the TQT texture uses...

GFX->setTextureStageAddressModeU( 0, GFXAddressClamp );
   GFX->setTextureStageAddressModeV( 0, GFXAddressClamp );

That (I am assuming) makes the texture not tile. So I tried that, and no difference. In fact I tried running it with GFXAddressClamp and GFXAddressWrap - and it didn't seem to make a difference in how the results came out.

I also tried just scaling the coordinates. A quick count showed me I have 16 "tiles" of that shaded texture being overlayed on my terrain. So I thought "OK, scale the IN.texCoord by 16". Results unfortunately aren't right, and look like this...

The scale looks right, but as you can see it's only sampling a 1/16 square texture now.

And so dear readers... any suggestions on which coordinate I need to be using here to pull out the right pixels from my "overall" texture?