Given the number of resources on the map, I think that we have to build too many outposts. I suggest increasing the outpost's ZOC radius by 2, to a total of 4 squares.

Also given how fragile outposts are and how easy it is to pillage the resources they supposedly protect, I think changes are in order. First, outposts should be granted free militia units like cities. The number of militia units can be a function of the number of turns the outpost was up, or some other factor. Second, all resources within the outpost's ZOC should be protected by the outpost, meaning that if an army onto a resource to pillage it, it automatically fights the outpost's garrison.