If you practice at 20 yards or less, then that ought to be your limit. If you practice longer range shots, then those could be your limit.

In fact, longer range shots are less likely to disturb the game than close range shots so the chances of missing either are comparable. For that and a few other reasons, I don't think there's an easy answer to what ought to be an "ethical" range. That puts a lot of responsibility on the individual but then that's where the responsibility should be in any event.