It could just be a matter of weight distribution and frame flex. With the eflow the battery and rider weight are on the seat-tube, that may cause more flexing at the sensor mount. Stromer is a very beefy, rigid build and the battery is on the down-tube. More flex can be good for some and more rigid for others, there's good and bad in most designs. The good in both bikes far outweighs any bad you could find.