Just to update this, I have been trying a few things to improve the signal quality, and I have finally settled on the following.
I have found that a 24cm length of 4mm² (AWG 12) speaker cable seems to work best. I tried a longer and shorter version of the cable, and also different types of cable including coax, but settled on speaker cable at a length of 24cm as @Joern initially advised .
The cable is attached to the base using heavy duty double sided tape along the top, the back and also the opening on the back.
Also removing some insulation from the end of the cable near the opening on the back of the base has made for an improvement in signal quality.
It’s important that no bare metal part of the cable touches the wheel base housing.
Bending the cable upwards on the steering wheel end of the cable has also improved signal quality.
I am seeing signal strength between 35 to 80 depending on steering wheel location with it set up this way.
Hope this helps someone, and thanks @Joern for bringing this ‘hack’ to my attention!