oh I also went looking around maya trying to think of what it might be.. when you press the cheaker button next to the color, it brings up the Create Render Node window. and I noticed that I have the "With New Texture Placement cheaked. and also in the 2d whare the file node is that you want.. at the top it has selection marks for Normal, As Projection, and As Stencil. I belive you will want the Normal one cheaked.

so I think you might have the Projection or probly Stencil cheaked as I belive that would let you specify the size of the texture. which you shouldn't have to wory about.