RFID behavior with aluminum
Basically RFID technologies powers the RFID chip by inducing an electromagnetic field as the principle of a transformer, where the reader is the primary and the RFID is the secondary coil. Also common wireless charging or inductive heater works this way.

When a conductive material, like an aluminium foil, is placed nearby, this electromagnetic field will be absorbed by the material and be converter in Eddy current which will convert into heat on the material, although the power of RFID is small, no noticeable heat will be seen.

Since the aluminium foil has lower impedance than that of the coil+electronic of the RFID, most of the magnetic field will be absorbed by the aluminium, leaving very little for the RFID.

This is why, RFID won't work, even if the foil is below, because most of the energy sent by the reader will be converted into Eddy current into foil and the RFID chip won't be able to have enough power to power up and transmit data.