Can I use a RFID reader to check if there is an physical obstacle between it and the tag?

I am trying to create a cheap system that check if there is someone sitting on a chair.

I would like to know if there is someway I can configure a RFID reader so it identifies when there are interference in the radio signal from a RFID tag caused by an obstacle - in this particular case, a human body. So I can put a RFID on the table and a RFID tag on the chair. I read it every 10 seconds, and when there is a human body (or any phisical obstacle) it notice some interference in the radio signal and register that that chair is occupied.