can you try ftpytail v1.4 from latest 1.2.2 beta ?
http://github.com/courgette/big-brother-bot/blob/master/b3/plugins/ftpytail.pyv1.4 forces FTP binary mode which is required on some FTP servers to get the SIZE command to work.
Else, if you do think the connection lag is an issue and hit the timeout, then you can tweak the timeout value from the b3.xml config file as such :
create a plugin_ftpytail.xml file :
<configuration plugin="ftpytail">
<settings name="settings">
<set name="timeout">60</set>
<set name="maxGapBytes">1024</set>
</settings>
</configuration>
Then in b3.xml make the ftpytail plugin use that config file :
<plugin name="ftpytail" priority="6" config="@b3/conf/plugin_ftpytail.xml" />