1.Start the Editor.
2.Choose Altis/stratis.
3.Insert a Rifleman as Player.
4.Get inside of any building and climb up to a floor above(works for any floor above ground floor).
5.Go crouch.
6.Adjust stance to 1 lower (default is: left ctrl+S).
7.Hold lean right key.
8.And finally aim down with mouse (you can do it with iron sight or without, doesn's matter).