Jim, AC6XG wrote:
"Would it be fair to say that you don`t agree that only physical
boundaries cause reflections?"

A transmission line may be terminated in its surge impedance, yet
somewhere along the line suffer a discontinuity producing an impedance
irregularity and subsequent rteflection.

The line may be matched to its final load, yet have reflections on the
transmitter side of the irregularity. Terman illustrates this on page
118 of his 1955 edition.

Terman suggests several reflection possibilities::
"sharp bends, insulating supports, resistive joints, coupled circuits
and extraneous objects" as typical irregularities.

I am not persuaded that reflection is caused by anything other than a
physical discontinuity, but Terman includes "coupled circuits" in his
list, and I think this indicates a physical discontinuity may be
referred to a reflection point from elsewhere.

Best regards, Richard Harrison, KB5WZI