[syslog-ng] Problem with hostnames!

Hi All! I am using Syslog-ng with php-syslog-ng. to give names of my choice to different hosts IP what i did was to define hostnames against each IP of host in /etc/hosts file. It was working fine with Public IP adresses.. But I have some hosts on local network too with 192.168 IPs . The pRoblem i am now facing is that its not storing logs with HOSTNAMES of private IPs. Where as its working fine and giving names of Public IPs. Any body has any idea?? any thing to do in configuration of syslog-ng?? Regards, -Geni