Which is why empires were all spherical and hadn't used natural borders extensively.
Why yes, many empires have been roughly spherical. Not completely, obviously. What we would do is use the river in the west to cut off the HK and build forests to discourage the TH as we extend down the river and east of it. We gain a natural border while living along land that is much easier to travel through, and thanks to our ability to grow forests that doesn't hold true for our enemies. We can also revitalize the land to the east a great deal more, thus not being a long line of needing to take nothing but border provinces.
It's pretty simple, if we take the land south of the eastern hills province then the eastern hills province has one border it doesn't have to worry about that isn't on the exact opposite side. of said province. Furthermore, we would be exerting significantly greater influence on the area to the east of the river, as they see our fertile fields and lush forests, they will be tempted to join our land. Just going further east means that people have to travel farther to reinforce further lands that have more borders.
Our increasing wealth would also greatly encourage various minors to convert to us, rather than the TH who just like to raid and the HK who say 'follow us or die.'
This is literally wrong.
From last turn:
New Settlement - There are a few new sites that could have new settlements placed on them: a new settlement within Redshore (can go further south), within Northshore (further to the west, inland to the north into the plains), badlands, eastern hills, northern pastures within Stonepen
North Shore is the former fishing minors, not Redshore. Do note that it says immediately before that that Redshore can go further south, saying nothing about further north.
We're adjacent to enough unoccupied hills to double our territory. They're maybe short on water, but we're not exactly that far from unlocking aqueducts.
If we're talking about the eastern hills I'm okay with that, I'd just like to use it as a stepping stone and start getting diplomatic inroads towards the lowland minors as we do it.
Keep in mind our diplomacy is a very large advantage we have (it's pretty obvious everyone else isn't seriously diploing) it would be great for us to leverage it while the HK and TH decide how to deal with each other.