>If yes, you have 1/2 of signal circuit missing or blocked and using only the wiring in the walls.
Not true! The conduit should be an excellent radiator for the airborne signal as long as it is earth-grounded.
Again, please use your ohmmeter to measure between the U-ground or conduit and the wire that feeds the TMCC signal to your layout. This should be an open circuit, i.e. near infinite resistance.