Internal API Management with vNet Integrated WebApps

Hi, 

I have deployed API Management on an internal virtual network. The APIM is fronting a load of AppServices (WebApps) that are all enabled with vNet Integration.  My question is how is the APIM calling the AppServices over the internal vNet if the backend service on APIM is pointing to https://mywebapp.azurewebsites.net? Wouldn't this call still be over public internet? Or do I also need to enable service endpoints on the APIM subnet for AppServices?

Thanks