Hi David,
.Net Agent can only track requests after IIS has forwarded the request to the Managed Pipeline. What you are looking for is End User Monitoring described in following document.
https://docs.appdynamics.com/display/PRO42/End-User+Monitoring
https://docs.appdynamics.com/display/PRO42/Browser+Real+User+Monitoring
After you enable above, you will get Browser Snasphots (taken by JS Agent) which will correlate with server snapshot (taken by .Net Agent)
-Raunak