Tedburn, what I can confirm is that the leaves are very hardy. They were full of dark green somewhat glassy botches after a few days of -8°C (17,6°F). But very soon they regained their normal color and survived unharmed. Well, -8°C is not really deep frost but the behavior of the leaves showed to me that they have a unusual / special ability to recover.
Thanks for sharing your experience with -16°C (3,2F°). A lot may again depend on the special conditions. Passive protection is certainly much better than none.
The fruits, by the way, are kept throughout winter and continue growing the next year. My experience with hardy citrus is still limited but this seems to be a rare feature of Poncirus hybrids. My Morton, Trifeola, (pure) Poncirus and Batumi Citrumelo trees drop the fruits in autumn or early winter no matter whether they are ripe or not. Ok, Keraji Mandarine also keeps the fruits throughout winter. But it is not a Poncirus hybrid.