I like your description of people having masks as "chin warmers" as I see this all the time.On Great Northern. It was about 50% correctly wearing on a lightly loaded train. Of the ones who were not about 50% had them on as chin warmers so maybe ready to put them on if the train got busier.
I live in a Transport for Wales operating area near the border with England. I notice that on TfW services mask-wearing seems to have declined but is still about three quarters of passengers wearing them on the Cambrian Line. However, once you arrive in Shrewsbury the people getting on there to go to Birmingham or who are using TfW services to Manchester, Chester, Holyhead etc are not wearing them so much. It's a bit of a vexed question about "we are in England and we don't have to wear masks on trains any more" or "you must wear a mask on this train because it is operated by a Welsh Transport Company."