I'm not sure if your tests will actually mean anything because I have a few harts and they all act differently. Even the same models .
Where I have noticed a difference using one or two hands is say I am honing a blade and not quite getting a part of the tip, I can swap to a single handed stroke and bingo I am then getting that part I was missing.
That is just an example I can remember from a long time ago but I know if I am struggling and trying every thing swapping from 2 to 1 hands will be some thing I will try.
Nice blades btw ..