Does the position of ATE caliper pistons matter?

Taking apart the rear ATE pistons and replacing the seals. Does the position of the piston matter? The top edge of the piston that presses the brake pads together is not flat all the way around.

Yes, to properly set the pad toe-in, for avoiding chatter. Template should be widely available.

There's a tool to rotate the piston and one to align it. Let me know if you would like to rent them.

http://hiperformanceautoservice.com/images/ATECaliper%20PistonTools9992918_9992919jpg.jpg

Missed that actual angle (20?) , if you want to "wing it" without the tool.

Basically, the "open" part of the piston is at the leading edge (bottom) of the pad, greeting the rotor as it rises up to meet it. (I assume) that counterbalances the pad's tendency to slightly rotate and "dig in" at the leading edge, keeping the wear even across the pad's surface.

If you got the Ate seal kit, it's in the instructions. It's very simple.