Cadence and speed monitor on rear wheel?
The Polar 200 user manual says that the speed sensor and the cycling computer must be no more than 30-40cm apart.

The cadence sensor attaches to the frame, near the pedals.

You could test how far away the speed sensor will transmit by just moving the computer away from the bike with the front wheel spinning. If it works at 1 meter distance, then putting the speed sensor magnet on the rear wheel and moving the sensor is worthwhile.

It could be that you'll need to juggle the orientation of the sensor and the computer to see how they work best.