Shirts that don't fit right, aka-Boob Triangles

I just want to mention this because I put a shirt on yesterday that had decorative triangles on the upper part of the chest.
Why are boob triangles not adjusted for the size of the shirt? It appears that I buy a larger size shirt so that it looks normal on top, but it never does. My boob triangles are always higher than where my chest ends.
Does anyone else have this problem?