Deault image size / scale

A quick test made inserting in a score two images of equal sizes, one raster (.png) and one vectorial (.svg) gave the following results:

Initially ("Size is space" checked):

After un-checking "Size is space" (without any modification to the image):

(Notes:
* for raster images, the resolution stored in the image is irrelevant: I tried two .png with the same contents, one at 72PPI and one at 300PPI and both gave the same figures as above;
* in case it is relevant, the score had a default scaling of 1 sp = 1.764 mm).

I know that in MuseScore vectorial images in "Size is space" mode have a conventional resolution of 10 pix/sp. It is a convention, it is documented somewhere: I'm happy with it (vectorial images do not really have a physical resolution).

For the rest, I do not understand three points:

A) Where the other 3 resolutions (16.6 pix/sp, 3.226 pix/mm, 5.348 pix/mm) come from.
B) Vectorial: if 10 pix = 1 sp (in space mode) and 1 sp = 1.764 mm, why 1 mm != (10 / 1.764) = 5.669 pix (in mm mode)? (and similarly for raster images).
D) Why a freshly inserted and un-modified image does not have a scale of 100%.

Questions:

1) Does anybody else think that a freshly inserted should have a 100% scale (= un-scaled) regardless of mode? (sp or mm)?
2) Should not a pixel be a pixel, regardless the image is vectorial or raster? In other words: shouldn't an un-modified vectorial image show the same figures as an un-modified raster image (and viceversa)?

Am I missing something?
Am I too picking?

Thanks,

M.