LOL. 3000 ft is not particularly low. Is that AGL or Barometric? My point being that at 12,000 (for example) you should be able to lock and fire at around 7km. Lower than that mans you will need to be nearer to shoot. The missile motor will only fire for a minimum time period, and then the missile becomes ballistic (effects of gravity etc).
Understandably you'll want to be fairly low against some SAMs which will mean getting close - or find a nice hill to hide behind, get a lock on the TGP, duck behind the hill, come round again, slave MAV to TGP and shoot, then get behind the hill. You can do this from quite a distance depending on the terrain!