Actually I had to Set it to $HOSTNAME$ to make the service check command match the CLI test.
Check HTTP service > Host settings > X Virtual host = $HOSTNAME$
Service check command check_mk_active-http!‘–ssl’ ‘–sni’ ‘$_HOSTADDRESS_4$’ ‘$HOSTNAME$’
OMD[MYSITE]:~$ ./lib/nagios/plugins/check_http --ssl -j HEAD -E -vvvvv --sni 123.123.123.123 www.mydomain.com.au