You said you made sure the mounting bolt wasn't too tight. Likewise, don't let it be too loose. Ideally, you get the thing as tight as you can, then use a hammer and punch to center the brakes. On your Trek, it looks like the pads are mounted a bit off-kilter.

It's not absolutely necessary to get the spacing perfect on sidepulls; as long as they don't rub the rims and the difference in distances isn't huge, then they should be working fine when actually engaged.