Cecil Moore wrote:
But rho on the coax is zero.

Coax doesn't have a 'rho' - unless it's broken or damaged coax.

The impedance at '+' is 50 ohms.

By virtue of reflection from the 50 ohm load.

rho = (50-50)/(50+50) = sqrt(0/Pfwd) = 0
at point '+'.

The same is true at points to the left of point '+' as well. So what?

And that 50 ohms is a V/I ratio which, I assume, you would
agree cannot cause a voltage.

As far as I know, V/I ratios don't "cause" anything.

73, Jim AC6XG