I didn't really think much of it when I did my brakes, so I can't describe its location in much detail. I just noticed it, shrugged, fiddled with it till the pads were "right" and was done.

I'm pretty sure it's on the side opposite the piston.

Here's what i know - the pad will go in normally, and then it can either settle in slightly offset and be "wrong", or you can shift it with your hand and make it settle in all the way and be "right" ..

you can visually see when it's right or wrong because when it's wrong it won't look straight. The difference is very small but it's visible.

It's easy to get it wrong if you're not paying close attention though.