The values currently listed may be dated, as Icy and I went through those a while back. That may explain the percentage discrepancies. The numbers themselves are pulled directly from the SHN files, so you should be able to view them as well.
I know that the icon images are extracted from the NIP files, so they will all be virtually the same size. There is no set maximum size, but this relies on each user's discretion, as having an image take up the entire screen is not feasible.
Image upload link