HTTPS Health Monitor Question

Need assistance understanding how best to implement an https health monitor for an external facing website. My goal is to mark a pool member down when it's unavailable. I've read about how to create a custom monitor like "GET /default.aspx HTTP/1.1\r\nHost: www.example.com\r\nConnection: Close\r\n\r\n" and look for specific text in the response string, but slightly confused about behavior of this monitor. So... if I assign this monitor to a pool containing 2 web servers what happens. Does the f5 run this monitor for each pool member and mark a server down if it fails? If the monitor is looking at the DNS name for the site how does it determine which server is down? In my instance the DNS site name would resolve to the VIP (internally) so the monitor could potentially hit any server in the pool. Should I look at implementing https health monitors at the node level? I am running LTM 11.3.