OK found the Log settings now, but also looks like I have found a bug.
The following log files ignore the 'Log Path' settings which I have set to 'S:\Logs\' and places these new log files in 'C:\Program Files (x86)\SmarterTools\SmarterMail\MRS\App_Data\Logs'
bosh-xmpp.log
Ews.log
SignalRLog
Could SmarterTools fix this bug and have these logs placed in the location given for 'Log Files'?
I ended up with 36GB of logs in this incorrect folder on C drive within 14 days which almost completely filled the C drives capacity.