Slices - exact width and height

Is there a way in slice property to determine the exact width and height of a slice? This would be an easy method to get slice boxes of equal dimensions. See attached picture.
slices.jpg

Graphic slices are constrained against all four sides of the page, which is why you cannot specify the Width and Height. This also ensures that they remain the same size (and positioned relative to the top left corner of the page) if you change the page size. Unfortunately this does mean that it’s difficult to specify the size for multiple frames without doing a bit of mental arithmetic, it’s true.

It appears the slices come through with a transparent background. I notice when I post a graphic slice that had a white background in Dorico onto a shaded post, she shading of the post shows through what were white background (even in between staff lines) in the original.
https://www.steinberg.net/forums/viewtopic.php?f=246&t=189581#p1003351

This is not a complaint, just something to be aware of.