Howdy
In CAS the SASS handbook recommends setting pistol targets out between 7 and 10 yards.
I have been splattered by lead many, many times. Typically it is because targets are pockmarked and dented. Even if a steel plate is hung properly , so it is slanted back around 10 degrees or so at the bottom, if the surface is in poor shape; pockmarked, or warped because it has been hit so many times, there is no predicting where splatter may go. When a target is properly hung, bullets will shatter on impact and the splatter will be directed pretty much straight down. It is always interesting to watch the splatter after it has rained. If there is a puddle in line with a target, one can see a line of splatter impacting the puddle.
Target placement is everything. If the shooter is shooting a shotgun at an angle towards a target, it is almost guaranteed that spotters standing an equal angle away will be splattered by pellets.
This is why eye protection is required at all CAS matches. It is a good idea not just to have safety glasses on, but side guards for splatter that may come from an angle. When I am spotting, I always face the targets directly, so that a stray piece of lead does not make it past a side guard and hit me on the side of the face.
Even so, with Cowboy Action shooting it is a given that you are going to be hit by splatter. I have been hit by solid bullets that did not break up, but more often it is lead splatter. One time I had a piece of lead imbedded in my cheek and it took a few weeks before I realized it was still there, when it started to emerge from my skin.
It's pretty interesting when you see a whole bullet coming right at you. It has lost most of its energy but it is still moving fast enough that you can't dodge it in time.
Bottom line, whatever distance you choose, be sure to be wearing adequate eye protection.