LOS comms
Be aware that there are several HF frequencies in use in any particular area depending on time of day. Hailing an aircraft on HF via selcal is iffy at best when you have no idea which frequencies the HF radios were last tuned to.
Also, LOS is from altitude to sea level in most calculations. If the ground antenna is on a 400' hill then you can add 28 miles to the numbers. Similarly, between planes at high altitude you can reach out 450 miles or so.