At the very least both RX and TX should have 1/4 wave straight wire antennas
Adding a length of wire may detune the output stage if it's been optimised to suit the pcb track design and reduce the signal strength
I'm using one keyfob to control two motors...
Otherwise a home-made sleeve aerial might be the only option.
Those receivers are garbage
Or is there a simple way of boosting the performance of the receiver?
When using the FOB, you are the antenna. .....Paul