The zabbix agent startup script installed via the official repo ignores any user tunables via sysconfig

eg

if [ -f /etc/sysconfig/zabbix-agent ]; then
. /etc/sysconfig/zabbix-agent
fi

exec=/usr/sbin/zabbix_agentd
prog=${exec##*/}

should look more like

exec=/usr/sbin/zabbix_agentd
prog=${exec##*/}

if [ -f /etc/sysconfig/zabbix-agent ]; then
. /etc/sysconfig/zabbix-agent
fi

this allows modifciation of the exec variables eg for none standard location of config files or other cli switches