Mike, the manufacturer manufactured the boot rack for the OEM BMW suitcase (which I have) and if you want to use the said suitcase, that is the way you have to attache/mount the boot/trunk rack on your boot/trunk to be able to use said suitcase the way the manufacturer intended.Perhaps someone could actually ask the manufacturer
On the other hand, if you do not have said suitcase, it does not matter one iota which way you attache/mount the boot/trunk rack if you are only transporting sheep and pumpkins.......