The chain stay on my bike measures 83mm at the thinnest point. I couldn't fit the kickstand, it's too narrow. I guess 75mm is also too narrow?

My chain stay measures 25-28 mm in height, width a little less, and the mounting oval incl. the supplied plastic inserts just fit. For higher/thicker stays, the attachment probably no longer fits (well). For less high / narrower struts, you have some leeway thanks to the plastic inserts, otherwise you could improvise a bit with rubber bands or the like.