I saw a post somewhere else, where this was done. The original poster found that magnet spacing was critical. When he added more magnets, the sensor could not tell where the magnetic field from one stopped and the next one started, until he increased the diameter of his disk. With similar spacing, the PAS worked. If you wanted to keep the same disk size, maybe a magnetic shield before and after the sensor would keep the fields from overlapping.
So how does your PAS work? Mine will supply a certain level of power at each level, and quit when the pedal rpm hits the maximum rate. My 36V bike will do 12-14 mph, 14-16 mph , and 16-18 mph in levels 1 thru 3. If I doubled my magnets, it would still do that, but since it thinks I am peddling 2X faster, it just does it at a lower pedal rate. I don't know if that would be much smoother when just starting out in level 1.
I think smoother would be more levels, each set for lower power.