When I set the engagment distance to just inside the maximum weapon distance, sometimes my ships stay at that distance, but 4 out of 5 times they don’t.
For example, I have some extremely long-range frigates that use frigate missles with a max range of 1200. When I set their engagment distance to 1000, they completely ignore it and continue straight towards enemy ships until they’re 300 or so meters away. I’ve tried messing around with every combination of orders, dials, toggles, and anything else I can think of, but they always close the distance. About the only thing I haven’t tried is removing the engines.