Texture2D.PackTextures - attempt to determine if texture was scaled

Texture2D.PackTextures scales textures if they don't fit, and I want to avoid that by adding more atlases. The function output is an array of rectangles, so I tried to compare the sum of texture areas before packing, to the sum of those rect areas from output, but the results differ even if I add a single texture, which fits to atlas bounds.

My problem is very similar to http://forum.unity3d.com/threads/texture2d-packtextures-currently-decreases-quality-without-alternative.98177/, though I couldn't find an optimal solution for that.

Anyone had this problem?