There are threads that discuss how to position your bike -- if it has metal in it. In general, position the wheel over the exposed trigger lines -- preferably inside the circles. Some lights work reliably with this technique, and others don't work at all. Some lights have long delays even if they do trigger, so its useful to time the light. Apparently even a small amount of metal can trigger the lights if its close to the trip wires. For people on carbon frame bikes, I wonder if you could carry a small 6" wrench on a string and drop it along the wire. Then haul it up when you see the side yellows switching.

The real problem at a lot of lights is that the lines have been paved over. Still others you can see lines -- lots of them! -- with no clue which ones are the current active set.