I dont think it goes by how many acers you have. Just takes a good back stop. And Common Sence.
But thats just me.
The backstop they would need to cover less-experienced shooters would need to be bigger than the width of their property which is long an narrow. I think a face to face with them to see their set-up would be very helpful.
Providence, I wish I knew who left me the nasty note. I have canvassed my immediate neighbors. The reality is that despite that I live on 40 acres and they are shooting on 20 acres, there are developments all around us with people living on no land. It could be anyone from one of those developments.