The size discrepency is normal, in my experience. You buy a 60 gb drive and after is formated and a file system is made you computer may show 58.3 gb. That is because before formating it is 60 gb. formatting the file system takes space. So when you set asside 2gb and knoppix needs at least 2 you need to set asside 2.1 or such to make the drive after formatting meet the size minimum. Try this with any fs and you will get the same result.

Either that or I'm wrong.