you might want to consider putting the sensor in the front, since that bolt that holds the front brake bracket should be tightened really well...
just a suggestion, since i personally thought about doing the same as you did, but decided not to put it there in case i compromised the brake bracket, and i want to be 100% sure that the brake always works, lol.
i also didn't want to have to align the sensor every time i took the front brake off to clean, which i do on a regular basis, and i was afraid that the aluminum sensor bracket might break if i tightened it too strong.