[userbinator]

The minimal explanation is that TCP is "turned around" at a dumb proxy, but upper-layer protocols may go further before being turned around. Which is trivially avoidable by delaying the TCP response with the same timing as the upper-layer protocol (and doing so to the protocol above that, etc.)

[Sakura-sx]

The issue is that if HTTP is an extra 50ms than TCP for example, if you increase TCP by 50ms now HTTP is 100ms more. Basically it is always more no matter how much you increase it.

[userbinator]

Not if you receive the HTTP request from the client first, before any interaction with the end-host.

[JDye]

If the proxy can "see" the requests, then this isnt an issue because the headers can be trivially be modified.

The problem is that the proxies which are targets of identification - think proxies for large scale web scraping which use CONNECT tunnels - dont get to "see" the request.