Cecil Moore wrote:

That is the nature of EM waves, Gene. EM waves flowing
in opposite directions do NOT interact. However, their
reflected and transmitted components traveling in the
same direction can and do interact at an impedance
discontinuity.

Actually it's even more straightforward than that. They do interact
with a physical impedance discontinuity, and don't interact with each
other no matter which way they are traveling.

73, Jim AC6XG