Took a look at 1472D. So it turns out they list item 59, Hand Breadth, with data for Ground Troops as well as Aviators, for the usual 5% and 95% centiles. I mapped this out into the analysis spreadsheet, and computed a ratio for the data, as well as me.
Not sure what to make of this. I'd have to start with asking folks to report hand breadth, to get some sample sizes. But going with the 1472D as representative of the population (male, anyway, in this case) I'd guess it's good enough to establish a relationship, which I would summarize as "The typical hand breadth measures just under 50% of Hand Length."
My hands are on the small side (7.3" hand length) but my Breadth seems to be under the average for 1472D, at 45%. So my hands may fit on shorter grips than say someone with wider paws. Maybe that's why I like the P365, as compared to say Glock double stacks, but by these numbers there's not really a yuge difference.
And of course there's even less handgun sizing information based on Breadth, than there is on grip size / frame size / whatever, so other than trial and error it seems hard to offer a prediction on what will, or will not, work for someone, based on adding breadth to the metric.
Hmmm.