I don't think opening height matters with the Model Y because the entire hatch opening is cavernous due to the slanted opening.
I do however have two problems with the Model Y that my ID.4 did better (which to has a larger cargo space than the Mach-E - I test drove the Mach-E when I owned the ID.4)
1) The width of the opening is narrower on the Model Y than I'd prefer (matches your numbers above). Limits fitting wide things in.
2) The sloped hatch loses some cargo space and it's not easy to estimate how much is lost.
The flatter top and wider ID.4 had technically less rear cargo space but the square space is more usable. I think the Mach-E is wide but when I test drove it and examine the rear cargo space it felt smaller. I guess because it didn't have the length of my ID.4 so it felt like a RAV4 sized instead of an Outback (bad comparison but that was my first sense). Like cramped.
In short, the Model Y seems great for tall and lengthy things that aren't wide. The ID.4 is amazing for boxy/wide things because it is shaped more like a square box in the rear. And Mach-E is a shorter (length-wise from back to front) but a wider than the Model Y.
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Now owning a Model Y... it really does feel like a VW Beetle with in SUV form.