Oh, to line up I just use a very clean block and go slowly and carefully. I practice on a scrap to help me learn exactly how it looks when lined up. I don't understand how a stamp positioner helps when the die cut is so close to the size of the stamp. There isn't any paper to place the positioner on to hold the paper still.
Also, a stamp press can help for tricky lining up situations of many kinds. I have the Fiskars one but I forget to use it many times in which it would be useful!