If so, FTP.EXE is using PASV and could be literally using the entire ephemeral port range.
If so, PROXY/FIREWALL would be wide open to the range.
If so, EDTFTP would NOT fail.
Makes more sense that FTP.EXE is using ACTIVE mode and perhaps instructing REMOTE SERVER to use either port 20 or, heavens forbid, port 21, for which to transmit data.
When in ACTIVE mode, how does the code determine the port to instruct the REMOTE server to communicate on?