Have experienced when putting after market pads in that out of the set of 4 pads only one has the correct slot for the sensor to fit into and if you don't put it on the side with the sensor then you will have an issue of it fitting! I will own up that I made this mistake once and now check that the correct pad with slot goes in the right location!! I assumed when I did it that it was just a bad fit and altered the sensor to fit, dumb! I even had a set once actually from BMW that did not have a pad with the correct sized slot for the sensor within the set, just took them back to the parts department who went OOPS!!!!
Does my bum look good in this !