RFID is basically an application of radar, and as such suffers from an inverse fourth power dropoff with range. Radio is inverse square, but when you reflect it off something, you suffer that inverse square twice. So while doubling the range drops your received radio power by a factor of 4, it drops your received RFID response power by a factor of 16. To have more than a tiny range, you need a lot of transmitting power and a really good receiver.
