We (the right-coasters) have created an evironmental rules for urban conflict; haze.
The gist of it is:
-1 per range band beyond SR. Therefore, a model shooting into MR suffers a -1 RC, LR a -2 RC and ER a -3! It makes for an interesting addition, and makes sniping a bit harder.
As for other "urban" rules, there is Rough ground, imparting a penalty of half movment when trying to navigate through rubble. Further, there is the variable RC modifier of trying to fire through windows, long alleyways, and over the park bench. Urban rules are subject to any other rules (Arctic, Jungle, night, etc.) that you wish to add to the game.
For the most part, we never have level 0, plain environments. Environments are flavor-enhancers, as well as equalizers (Vulkans having to clear jams every other shot in the desrt).