Does this heighten ability actually… do anything? You can make the crawling flame medium instead of small, but size differences don’t have any inherent mechanical effect usually, and small and medium creatures take up the same amount of space. I guess grapple rules use size, can you grapple a crawling flame?
At least with the higher levels, the flame takes up more squares and has larger kinetic auras, but small->medium doesn’t really seem to do anything.