Rdrcr, I had the same ultra fast readings from my wireless at first. I remounted the sensor and magnet closer to the hub to close the gap between the magnet and sensor and it settled down, for the most part.

I don't think it makes a difference where the magnet is mounted. The magnet will pass the sensor in the same time interval whether near the hub or near the rim. The magnet is going faster when near the rim, but still attached to the spoke.

Brad