An interesting thread!
Related to the polarisation issue, but slightly OT:
Some years ago, with the re-shuffle of DTT muxes,
a powerful transmitter across the water was allocated
the same frequencies as our local TV relay,
but with opposite polarisation.
With tidal rise and fall, the signal was subject to
addition and subtraction of the direct
and the water-reflected signal, but also
- here significantly - to "tidal twist"
of the signal's polarisation.
Many locals received both signals on the same
channels and, consequently, very erratic reception.
QED : polar twist can happen.