A screen made of some conductive or low resistance material such as cooper, makes more sense to me to shield against RFI/EMI, however it posses one question;
How would this screen will affect the receive lobe of the antenna?
If using 2.4 GHz radio the wavelength becomes very small, therefore the likelihood of screening the RF energy coming form the transmitter may be very low.
I don´t want to find out if this is not true.

I still think that best way to shield against the RFI/EMI coming form the spark plug is by using the shielded resistor plugs.
This stops the offending source of this interference right there where it belongs, just where they are created.

If the ignition box or other components develops hot spots due to poor shielding, frayed RF cable shielding, lose connections, metal to metal friction caused by high engine vibrations, etc, then this is other history.

For any secondary source of RFI/EMI, use whatever trick you may think off, plastic servo arms, plastic clevis, phenol pushrods, etc.
Some may argue that they use metallic clevis and metallic push rods without any problem whatsoever, that’s fine as long as that works for them.

Distance is another way to get rid of the EMI/RFI, some may argue that they locate ignition vs. receiver or other electronic components close each other without any problem, that’s ok too. They may have a very good shielding built up in their respective ignition boxes or spark plug connectors, cables, etc. or ... lucky guys.