There could be few reasons. First the multirom selector menu takes 2M. Then, ROMs has to start on a natural alignment of their size. Meaning 8M ROM starts at a location in a cart that is dividable by 8M and so on.. odd sizes like 3M get rounded up. This basically means that the order ROMs get flashed to the cart matters. a 2M ROM followed by 8M ROM wastes 6M of space.. unless the flash utility is clever enough to put e.g. 3 additional 2M ROMs in that space... I don't know how Windows tool does stuff. Slim-e-loader for OSX has a simple algorithm that tries to optimize the free space in the cart.. just my 0.03 euros.
