Tests are also done under the worst possible conditions in an attempt to bring about any unwanted change. And since we don't have a magical box that lag can be contained in, it needs to be done in areas where it is already a problem. Its not about attempting to figure out some specific error, that can be done in just test-firing anywhere, its about testing to see if it still operates.
Operation in lag is not a controllable factor, and still necessary for testing at peak and base conditions. It will take more than one front in order to test weapons in all necessary aspects.
It is necessary to expand patrol provisions beyond the wall to stay away from the age old concept that other militaries have followed; being there a giant wall with a field in front of it where people spawn. It doesn't allow for any variable if everyone is just standing on the wall shooting at someone who has only one direction to go.
Yes, the Ordo Imperialis is funded by breakfast cereal sales, as well as other parts of a balanced breakfast. Majority market shares owned in a variety of milk and orange juice companies, as well as coffeee, as we all know. This, you see, is how you truly accomplish world domination; through the stomach of your enemies.