It's been many years since I implemented G.Hn hardware, but if memory serves the chipsets are typically able to split the available bandwidth into 1 or 2 MHz wide bins and choose different symbol densities and FEC levels for each bin. If you have a bin that has horrible reflections, you don't use it at all.

I also recall that the chipsets don't do toning automatically, and so it's up the the management device to decide when to re-probe the channel and reconfigure the bins.