VIP for syslog traffic

Hey All

I am trying to setup a VIP to collect syslog traffic from different type of network devices to some backend server in some random ports 1401 - 1408 for server with that specific VIP on 514 udp. So when I set the following

1. VIP protocol & client profile : tcp, snat : automap, health monitor : tcp ---> the logs weren't seen on backend server, thou on packet capture I could see the F5 was receiving logs. I saw server seeing an ICMP port unreachable from server to F5 VIP on port 1401 or which ever til 1408.
2. VIP protocol & client profile : udp, snat : none, health monitor : udp ---> the logs were collecting on server Note the server has capability of running on both tcp & udp ports ( 1401 - 1408 ).

Can someone help me explain what could be the reason of failure on 1st scenario.