OPK: thin vs thick lines?

Hello! I'm still getting the hang of OPKs, and am totally confused by what it means if one line is thicker than the other. For example, sometimes the shade of the test line is as dark as the control line, but it's thinner, which makes it look lighter. In this case would it still be positive? Or should it be as dark AND as thick to be positive? Thanks for any feedback y'all can provide!