I think that the 400yd limit poses, first and foremost, a safety issue.
Looking at that tire stack, I see it as an excellent safety measure as well as noise control; because it imposes a tight channel to the trajectory, Bullets that disperse significantly from the POA will encounter tire sidewalls.
One thing I've seen with tire stacks is that they tend to acquire bee/wasp infestations, which tend to get mightily pissed when on touches off a round right next to their home. Keep bee/wasp spray handy and pretreat the stack before setting up.
Still, the stack provides a significant deterrent to leakers from the intended trajectory. It could ensure that the beaten zone is concentrated onto the berm.
What about insurance; and how would baffling such as I describe affect insurability/premiums?
Greg