I think you have asked the wrong question. I would say what is the shortest indoor range you would be happy with. a lot of air weapon target shooting is done at 10m but what I want is a 100m full power rifle rated range than I can shoot anything at any distance I desire. What I will settle for is 20m minimum.
I think a lot of the indoor 100m ranges were in disused train tunnels but mushroom growers are willing to pay more than a range can afford so they became mushroom farms