As it stands, we have definite borders to wherever our settlement exists. We can not build beyond it.
I have heard rumors that we can secure multiple monoliths, but I have never seen this confirmed. Assuming it's not true, then I'd like to know our base has potential for greater size, and I have a simple solution for how.
I read once that the strength and prosperity of a society can be gauged by how much power it consumes.
If we have a camp whose only source of energy is a campfire (which would actually be a totally cool addition!), then obviously it cannot be very large, nor powerful. But if we are running multiple reactors, as well as operating a field of windmills and utilizing local power wells, could it not be said we are a well established civilization?
I suggest that a base's total power consumption equate to the range of a monolith's influence. While a linear increase in influence may be abused by power-happy players, maybe a gradual exponential increase in the power needed to create influence is all that's needed to tailor off this potential problem.
A simple mspaint graph I've attached shows that short-term influence gains are simple enough, and will satisfy most ambitions, but for a truly vast empire to exist, a very powerful effort must be put forth in order to compensate for the exponential hurdle.
http://www.loveinvers.es/sites/default/files/InfluenceChart.jpg
Also, I'm pretty serious about campfires. :)
Monitor lizards fear fire.