Thanks for the update.
I'll have to pay more attention to mine and see how long it takes to get a new reading. I'll let you know ...
Antennas are funny magical things and not my expertise. But, I would guess that the power wiring of the receiver plays a part in the reception.
Wrapping/spiralling a wire around and along the power wires (not physically electrically connected) and then running it towards the rear of the bike might aid in the reception of the rear transmitter. Just a wag, and a pita, but a thought ...
Edit: My wiring is easily available. I may give this a try and see if it helps in the next couple of days ...