Interesting question, Jim.
My hearth is 107 cm high (a lot higher than planned, because I forgot to allow for insulation
) and I'm quite small (158.5 cm) so that gives a ratio of 0.68.
I was worried it would be too high to build fires comfortably and thought I'd put in a step if necessary, but it turns out that it is a really comfortable hight for cooking. I certainly wouldn't want it lower if I did it over again.
So to get the same relative height, your hearth would have to be 48.6 inches (or 123 cm), right?
Have we got any phisiotherapists on the forum who could tell us what the ideal height should be?