Merging a Texture of Set Resolution with an Imported Texture

I'm running into a problem where I am trying to merge two textures together, one that is from Application.ScreenCapture and another that is a custom overlay.

In my code, I successfully combine the two images, but i run into an issue with the overlay. The screencapture is a set resolution (the screen size or, in the case of my testing, 1920x1080) and the custom overlay is also a 1920x1080 pixel png. When I import it into unity, I set the max resolution to 2048, and it seems that Unity imports it then as a 2048x1024 image that is in line with the power of two.

I'm not really familiar with power of two or why Unity does this, but it cause an issue because now the overlay does not match the screen capture. I have a 1920x1080 image that I am combining with a 2048x1024 image into a 1920x1080 image. It results in the resultant image being offset due to matching pixel to pixel.

Is there any way to force a screenshotted texture to 2048x1024 or force the 2048x1024 import setting to 1920x1080 so that they match?

Example Background: http://i.imgur.com/RIBsozh.png Example Overlay: http://i.imgur.com/K0cFW3M.png Example Output After Merge: http://i.imgur.com/8XkznBN.png