The tab goes where the geometry of the fork blade dictates. Unless the fork blade runs perfectly plumb from the crown to the dropout, there will always be some offset between the top of the tab and the bottom. If you have to bend the tab to get it to land on the blade in your preferred location, you are just adding an angular force to the attachment point. and a higher chance that your tab is not in the same plane as the rotor.

As Andrew said, as long as you are not pushing the limits with the blade thickness, the tab placement doesn't really matter. I don't have any better pictures of the brake tabs, but the tabs on this fork are just individual tabs welded onto the .049" wall 3/4" tube. That fork has seen hard use on my MTB with a 180mm rotor for over 8 years now.