[MxxCon]

[list=1]1) these "anti-fragmentation" options are nothing more than a myth.
such option does not help reduce fragmentation simply becuase even if you create a dummy file and will try to write data chunks on top of that dummy file, it does not mean that windows will write data on to exact same place. windows will write data where ever there is empty space and will free up "overwritten" part.

2) creating one large dummy file and then filling it with data will make it impossible for other ftp clients or flashfxp to resume downloading such file. since in ftp there is no integrity hash checking, how will flashfxp or any other ftp client know that that it's a "dummy file" and not actual file filled with zeroes.

3) you are thinking in "p2p" terms where clients download chunks of data all over the place and then assemble final file, which can, but not nessarly will, be fragmented.
ftp transfers work with data sequentially, start reading/writing from byte 1 and end in byte 'last'. if there is enough free unfragmented disk space on your hd, that file will not be fragmented.[/list=1]