Do light probes light objects per vertex?

Hey guys, I'm having problems lighting a large object with light probes. I'm trying to make a train get light by multiple lights as it goes by. It's kind of like a train going through a tunnel that has lights lined up on both sides.

(lights like this https://www.youtube.com/watch?v=Igin3eoOOoA)

Here is some testing that I did to try to figure out the problem.

The yellow dot that I drew in represents the 1 pointlight that I used to bake the lightprobes. The cylinder and the grid of squares are reacting exactly how I was expecting the train to react. Once I saw that those objects worked, I thought that maybe light probes were based on vertices. So I subdivided the train to add more vertices. To my surprise, it didn't work. I then added a huge plane with lots of divisions into the scene and noticed that it was also getting lit 1 whole color instead of a gradient per vertex (huge square plane).

Anyone know why this is happening? Or how to fix it? :)