The fitting size should be the length it spans between cards, not how far away the cards are. Since it's going over 2 slots (PCI-e x1 and the other x16), it should be a 2 slot connector.
Like I said before, the easy way to confirm this is to measure the approx. length and compare with the dimensions of the connectors. I would recommend this if you're not 100% confident in the one you're looking at purchasing.