Visual horizon Pontius Navigator
This question came up about 3000 posts ago. 1.23 X square root of height was posted. I always used 1.25 since that was easier to do mentally ( only had whiz wheels for math back in the 60s!) and we needed to know PDQ when we were looking for the odd Bear D or Badger inbound to the carrier.
Actually Pontius I started this to remind you that the correct term is"Anomalous Propagation"
AND it's real. I've been flying in the North Malacca Straits between an upper and lower inversion acting like an enormous wave guide and seen returns from way outside my normal radar range