I must say there seems no logical explanation for it. However, my square 200 x 90 link units out perform the Horizontal link units BIG TIME. The click through rate is a little better, and the pay per click is 2 times. They appear to have about the same terms but there is just a big difference in pay per click. Anyone else experience this or know what could be the reason? I have been experimenting with this a while and it has held true for months.