You win the cigar... 'Ducting' or 'Tropo' as we hams often call it
acts just like the furnace ducts in your house in guiding the air that
wants to spread everywhere to where we want...
With VHF radio signals sharp temperature and density gradients in the
atmosphere will act just like a metal duct, forming a roof and a floor
and causing the radio signal to skip/bounce/reflect as it goes along
and confining it like inside a heating duct (actually it refracts but I
don't want to go off into theory here) forming a roof and a floor...
Usually the floor is the ocean or the ground and the roof is a few
thousand feet in the air... Other times it is another air discontinuity
layer below the upper one and when this happens the signals will rattle
along for thousands of miles losing very little energy... If you are
in the right location when the signal finally exits the duct you will
hear strong signals from far off...
When hams discovered this effect in the 50's and 60's (the big time
physicists of the government denied any such thing existed) the first
evidence came from 2 meter ham signals being ducted between Hawaii to
California (how's that for line of sight vhf?) But, to transmit or
receive these signals the hams at each end had to go up the coastal
mountains (usually in their car) to the correct altitude and that duct
could be as narrow as a hundred feet in height... Higher or lower and
you were out of the duct... It was first noticed by hams who just
happened to be driving the mountain road and suddenly began hearing
signals from Hawaii - a happy accident...
Anyway Paul, a good call on your part...

denny / k8do