Dimensions in draw.io

[Michael Lambert]

I create a new diagram using US Letter paper and set the grid to 18 points.  In terms of PostScript points, the page is 612 x 792.  Thus, I would expect the grid to be 34 x 44 with major grid lines being 8.5 x 11 (the paper dimension in inches).  However, what I see is a major grid that is roughly 11.75 x 15.25.  In order to make the grid fit as expected, I either have to set the Page Scale to 0.72 or set the grid to 25 points.  Based on https://en.wikipedia.org/wiki/Point_(typography), either of these is consistent with a draw.io point being a CSS q point (0.25 mm), not a CSS pt point (0.3528 mm).

My question is what is the definitive size of a point in draw.io?

Thanks,

Michael