I used to fly level 4 missions in a Rattlesnake. The process was land, MJD away from rats, drop sentries (Wardens). I would orbit the Sentries at 5Km.
Both Wardens (2X Omni II with range script) and cruise missiles had an effective range of 150Km and that was also my lock range (Sensor Booster II). I could use cruise at 150Km but my drone control range was only 105Km (2x DLA II) so the Wardens wouldn’t fire until the rats came within my control range.
I sold the Rattlesnake 2 years ago - my game has moved more to industrial play and things may have changed, but in my experience your target needs to be within your drone control range for sentry drones.