Texturing and glCopyTexImage2D

Earlier this month, someone posted a question about why glCopyTexImage2D() yields a texture that when bound, is greater (or smaller for that matter) than the original image (which came from the GL_READ_BUFFER). Now i’m wondering how to get around this, or how to modify my code so that the texture does not shrink or grow depending on the size of my polygon. Is there a way to do this? Thanks!