"...appear to have used a higher than speaking voice."
Do we know this is the case with Joseph Taylor Paul? I know the Grainger collection pretty well and I wasn't aware there was enough of his speaking voice to make a solid judgement on its general pitch.
I do know that the spread of tension is one of the major factors in over-pitching (not suggesting that Taylor was either overpiching or tense, though I have heard it suggested that the apparent vibrato in his singing was due to nervousness.
There's a story conected with Grainger's recording of the Brigg singers.
It is claimed that, after singing Lord Bateman, George Wray asked could he hear the recording. Grainger duely obliged and Wray stood scratching his head and finally said "That bugger learned it a lot quicker than I did".
Jim Carroll