If you need more support because it's in a high G area or the span of track between supports is greater, thicker supports help. In the linked image I've attached, the support in the background is under a heavier G load than the support in the foreground (and the diagonal bean you see in the uh.... fore-est foreground), which is in a floaty section. They have roughly the same span of track between them and are nearly the same height but not quite. Also the single pole with the stairs around it is for the block brake (remember it's by itself, it's not an A shape and has no diagonal beams coming out of it), where not much in the way of G's is happening and you can compare its thickness as well.
I'm not an engineer though they'll know better. This has to be loaded with situation-related exceptions (earthquakes, supports dodging something, etc). Hope this helps.