Does anyone know if it expects the partition to be exactly that size?

The partition doesn't (currently) have to be exactly that size. After the 2Mbyte mark, the rest is used for dynamic data, one sector per tune. Unless you have 28,672 files on your player, it doesn't need to be that big.

Of course, as the format isn't "user-visible" in any way, we might well change it in the future (to allow for persisting longer playlists, for instance). But we won't be changing it before 2.0final.

Peter