the CSM doesn't do syn proxy by default.
If you see the CSM doing SYN proxy it's because you have configured a feature that requires the csm to proxy the connection in order to accomplish its task.
Basically, L3 or L4 rules are not proxy.
L5/L7 rules are proxy.
If you do cookie, url loadbalancing, ssl sticky, ... the CSM will proxy.
Regards,
Gilles.