Hi Greg,
There is an updated radio receiver module for these (it sits right hand side, just behind the rear seat release button, remove the right side parcel shelf support) about £120. This has a much better interference rejection performance, it also reduces the tendency for other vehicle key plips to wake the BeCM and therefore cause the battery to go flat. I think it will probably help the key signal to get through in high noise situations.
As far as I know the reader coil around the ignition switch is only a transmitter, the mobilisation is returned via radio to the receiver at the back. Plipping right next to the rear window may have worked.
Will try to look up the part number when I get back to work.
I always advise my customers to have one fitted.
Shaun