Actually, in my games forts go down very fast, you can take small Maginot lineof Checks in 1-2 weeks of fighting. There is no need to build land forts ever in this game, as for the same IC you would get much more defensive power from units. Even in the in a province defended by 20 division, a single level isn't as good as 1 aditional infantry division, because it goes down so fast. I hope the developers will look into it.