Reg, G4FGQ wrote:
"It`s purely a matter of Spherical Geometry"

Edmund A. Laport agrees with Reg in his book "Radio Antenna
Engineering". On page 227 Ed writes:
"If, for example, the computed vertical beam angle for a one-hop circuit
uses 6 degrees at an azimuth of 332 degrees and the horizon in this
direction consisted of a mountain range with a height of 8 degrees, the
performance of the circuit would be greatly compromised by the
obstruction of the mountains. In such a case it might be better to work
this circuit with two hops. Then a vertical beam angle of 20 degrees can
be used instead, with adequate horizon clearance for the wave path. Or
if the circuit required 6 degrees for a two-hop circuit 5400 kilometers
long, with the same obstruction cited, one could change to a three-hop
circuit which for the same layer height would permit the use of a beam
at 14 degrees."

Best regards, Richard Harrison, KB5WZI