If you want to get an estimated RSSI based on the signal % value, I have been using the following formula in vistumbler
$InSig = Signal % Value
$dBmDissociationSignal = -85
$dBmMaxSignal = -30
$RSSI = ((($dBmMaxSignal - $dBmDissociationSignal) * $InSig) - (20 * $dBmMaxSignal) + (100 * $dBmDissociationSignal)) / 80
If you look at the latest beta (10.3 Beta 16 right now) I have updated the native wifi UDF I use and started to implement RSSI, Right now it is only available in the gui since I have not updated the export formats yet (this should happen before the final release)