I don't think that having "camping" aliens scattered around the map necessarily is going against the principles of military strategy. Sure, throwing everything you have at the enemy all at once is one effective strategy, but lying in wait and ambushing the enemy is also an effective strategy. This idea could have the potential to be really fun if the "campers" were placed in effective locations, behind doors, in the aforementioned nooks and crannies of farmhouses, and would create those memorable moments of surprise that this game seems to be lacking at the moment.