I'm not sure if the AI can differentiate between what each one means... Whenever I use them, they just seem to blob everything to that area, regardless of what ping you gave them.
Also, I'm not entirely sure why, but there are times when pings won't work. Usually this happens if you ping a location that you don't currently have revealed through the fog of war (this might be just me), or if you try to ping enemy base sectors. The best thing you can do is progress with the AI: reveal territory, move your units up, and ping for your ally to reinforce you.