Tam, WB2TT wrote:
"There is almost always some kind of enhanced propagation."

True. It is also true that a 10-element beam and high power extend
transmission range.

Terman has eqn. (22-7b) on page 820 of his 1955 edition:

"Radio horizon distance in miles = sq rt 2h
Again, h is in feet."

Terman also says: "In the special case of the standard atmosphere, k =
1.33 and the horizon distance becomes, miles = sq rt 2h."

1.33 means the earth`s radius appears as 4/3 the actual value.due to
atmosphere causing the radio horizon to be more distant than the optical
horizon.

On page 825, Terman says:
"Fading is most pronounced when the received signal is much weaker than
the free-space value for the distance involved. Thus fading is usually
greatest near the radio horizon and in the shadow zone, and tends to be
small when a "good" optical path is present."

My experience agrees with Terman. We all know that VHF propagation does
not always follow the simple rules.

My contention is that path clearance outshines other considerations in
determining "How far can an antenna see?". Terman`s eqn. (22-7b) is the
usual answer.

Best regards, Richard Harrison, KB5WZI