2048 and 4096 may feel not being rounded, simply because you’re more familiar with base-10 counting; they are perfectly “rounded” in binary (base-2), as 2048=2¹¹ and 4096=2¹². Incidentally, 16,384=2¹⁴ is also a perfectly rounded binary integer. METAFONT internally works with UPM of 1,048,576=2²⁰, and our base-10 brains…