logging on interactive mode vs command line mode

Hello,
       I'm trying to get the logs (Transfer Percentage an ETA) by 
running in command line mode.
       Using xfer:log yes in interactive mode, I am able to get the 
output in ~/.lftp/transfer_log
       But if I pass this in the command line, I only get the latest 
line printed something like

2010-01-14 18:32:19 SourceFile -> 
ftp://xxxx:xxxx@yyyycom/ftpTestArea/TargetFile 0-2544495899 21.06M/s

       and also it only writes the file ~/.lftp/transfer_log after it 
finishes the transfer.

       Is there a way to change this behaviour?
       at the moment I'm using "screen -L lftp" to be able to write a 
file an read the logs at realtime using lftp in command mode.

Thanks in advance
Fedeirco