I tested it by closing openxcom, changing radar range, then re-opening it. I must have seen the values I saw due to having LARGE_RADAR_SYSTEM at 2100 and SMALL_RADAR_SYSTEM at 1800 by default. If I changed small radar to have longer range than the defunct large radar, it displayed as long range. But when it's back to 1800, the hyper-wave decoder must go as low as that value to list as short range.
Is it just taking the lower of the two values between the original two facilities and setting that as the minimum radar range?
What I want to do is to have four radar facilities:
Radar System: 1x1, short range, 1800 NM
Large Radar System: 2x2, long range, 2700 NM
Hyper-wave Decoder: 1x1, short range, 2400 NM
Large Hyper-wave Decoder: 2x2, long range, 3600 NM
Based on this information, the best way I can see to implement this would be to hold both the SMALL_RADAR_SYSTEM and the LARGE_RADAR_SYSTEM defunct and make four new facilities, using the old ones to set the minimum radar range. Is there a better way to do this that doesn't involve handing people a 2400 NM radar just for upgrading their mod version and/or would it even work?
