As you probably know, we are limited in our ability to detect mobile/tablet devices by the user-agent string and other HTTP headers that are passed in the image request; at present, the iPad mini has the exact same user-agent and headers as the "big" iPad, which makes it impossible to detect the mini as a different device. We are working with our mobile device lookup vendor and Apple to change this in the future, and as soon as it's possible, we'll do it.
