@Gary_H I pretty much shoot steel exclusively. All my targets are the swing type supported by chains to an extra tall 2 x 4 saw horse. Plate racks as you describe above are just not portable. That said I did have a battery operated falling LaRue target that was a mini silhouette that I traded for a rifle as it was more of a PITA than it was worth to haul around. I’ve not been fragged by my swinging plates but I have been hit by frags from “non-movable” steel such as the cross bar on a plate rack or a fixed target.
When I was setting up a range we had to make a determination where the safe line was with our steel. We set up paper around the target at various distances and shot the crap out of them with a variety of firearms. ~5 yards was where the hits petered out in the 90* directly in front of the target. Off to the sides we were getting hits to about 10 yards but A LOT more of them.
As an outlier, low velocity FMJ’s will bounce, sometimes at a fair distance. A bud of mine took a .380 ball round to the leg at 25 yards standing behind/to the side of the girl shooting it. She hit the cross bar of the plate rack at 10 yards. I bounced and missed her by 2 -3 feet to the left. Left a nice bruise on his thigh (similar to a paint ball hit) but did not penetrate even his pants.
If I were to set up steel for pistol exclusively I would make sure that they were swingers. If I had a plate rack or dueling tree I’d want to make sure that there were no non moveable perpendicular surfaces. The lower the velocity at impact the higher the chances for ricochets ESPECIALLY with FMJ or HP’s. Lead doesn’t bounce real well but I have recovered hundreds of lead slugs w/i 5’ of steel plates when shot at a fair distance, say more than 25 yards.
So 11 yards is a fair guess as far as a safety factor goes but there will always be some risk. Long sleeves/pants and EYE PRO are definitely required when shooting steel with pistols at closer ranges. Most rifle rounds will disintegrate at close ranges but some with hardened penetrators may bounce so if you are running a CQB type scenario with say “green tip 5.56 ammo” angle the plates just a bit to force the deflection to down range. IMHO you should do this with plate racks also, mebby a foot of angle for the length of the rack (assuming a 10’ rack).