I'm not familiar with this specific setup. A picture would help. Without knowing more, I can only suggest trying a larger/stronger magnet. I use a 3x12mm rare earth magnet that attracts and holds itself to the inside of the pedal spindle and lines up with the sensor. It can also be attached to the inside of the crank arm with 3m permanent outdoor mounting tape (grey foam), or adhered with some rtv silicone adhesive. I find this works 15+ mm away from the sensor.