Aftermarket and Factory Camshaft Postition Sensor

Can someone explain why an aftermarket CPS won't work with the 01 740IL's and the factory ones will? I haven't seen a new factory one yet but I did see an new aftermarket one. The only difference I see is the diameter of the part that goes inside of the chain housing. The aftermarket one has a larger diameter "probe" portion, thus more magnetic field signal to the computer? Thats the only thing I can think of. The must have the same circuitry as there are 3 terminals on each so that shouldn't be any different.