I have found Flyer Chief need line of sight for the signal. They will operate for a short time when not in sight. I have a plaster mountain on one end of my layout and when the Berks are on the far side of that they continue to operate, same with the GP. I don't believe that the tender mod helps the signal but it eliminates power interruption which may contribute to balky operation.
I should have mentioned the range of the signal is somewhat limited, with the orange controller, at 50 ft l still have control, but keep fresh batteries in the controller.