For an inductive coil... You can think of the electrical field made by the wire like a Slinky curled up into a donut shape. Your goal is to intersect as much of the Slinky's coils as possible. The best spot is along the edge of the cut, not right in the center of it. The triggering material needs to be
conductive, not magnetic. There are other kinds of sensors, this is for the kind that you can see the saw cuts where they installed the coil. There are types that
do detect magnetic, we don't use them here in CA for the very reason they don't detect bikes.
Here's a good writeup from NC advocating that they do it like CA, and it has a good list of references at the end:
https://www.bikewalknc.org/bicycle-d...affic-signals/