I guess also when you play as a team you will stay together and not spread all over the whole map. Your movements depend on the objectives. There are very limited possibilities to let enemy spawn outside the reachable area.
I've always liked the ideas of enemy hiding somewhere and then being aggressive/ spawning in or having reinforcements attacking from locations that make sense like the forest paths in Alps1 or the nearby town in Czech1. When playing alone or in a small group, it makes sense for enemies to spawn from positions your just passed through... but it's not so nice when your team covers a wide area and the enemy spawns in your face
No problems for me, just a personal wish that missions can be build to keep the players in suspense all the time, even if not much happens in 15 mins of playing. That was the point of creating random stuff... not necessarily to overwhelm our team, but to always leave you wondering. You can always put the mission on Hard, 1 life and try to finish it that way.