Clarify what HTTP health checks target

reference/configuration.html.markerb

@@ -489,7 +489,7 @@
   path = "/"
 ```
 
-Roughly translated, this section says every thirty seconds, perform an HTTP GET on the root path (e.g. http://appname.fly.dev/) looking for it to return an HTTP 200 status within five seconds. The parameters of a `check` are listed below.
+Roughly translated, this section says every thirty seconds, perform an HTTP GET on the root path of the service, looking for it to return an HTTP 200 status within five seconds. The check runs against the service on the Machine over the app's private network, not against the public `appname.fly.dev` hostname, so it works even for services that aren't exposed publicly. The parameters of a `check` are listed below.
 
 Times are in milliseconds unless units are specified.
 
@@ -790,7 +790,7 @@
     [services.http_checks.headers]
 ```
 
-Roughly translated, this section says every ten seconds, perform an HTTP GET on the root path (e.g. http://appname.fly.dev/) looking for it to return an HTTP 200 status within two seconds. The parameters of a `http_check` are listed below.
+Roughly translated, this section says every ten seconds, perform an HTTP GET on the root path of the service, looking for it to return an HTTP 200 status within two seconds. The check runs against the service on the Machine over the app's private network, not against the public `appname.fly.dev` hostname, so it works even for services that aren't exposed publicly. The parameters of a `http_check` are listed below.
 
 Times are in milliseconds unless units are specified.
 
@@ -1013,7 +1013,7 @@
   processes = ["app"]
 ```
 
 When a machine unexpectedly exits, our scheduling machinery follows a machine’s restart policy to restart it without your intervention. These policies are quite similar to Docker’s container restart policies:
 
 - always: we’ll attempt to restart the machine no matter the exit code.
 - never: we won’t restart the machine even if it exits with a non-zero exit code.