FLASH file system capacity

NETOS 7.0. On a 4MB Connect ME “C” module I have defined FILE_SYSTEM_SIZE as 3072K in customize.ldr. For some reason, if I FTP files into the FLASH0 file system I do not get 3MB of capacity, I only get about 2.3MB. My image.bin is only 516K, which including the 2 64K bootblock and NVRAM sectors fits in the remainder and should give me the full 3MB. Any ideas why I’m not seeing that? Some sort of sector size limitation? What sort of FLASH file system does DIGI use anyway (NOR/NAND FLASH?). What’s this I’ve read in older posts about having to format it? (I assume that was in the NETOS 6.X days)