That's assuming the corporate proxy is well-behaved.

Then all bets are off, and I guess we just can’t HTTP ever again because a proxy can misbehave.

One should adhere to Best Practices since one cannot control every device between the app and the user. Best Practice says “GET has no body. QUERY can have a body. If QUERY fails (405), use POST with the body.” And eventually, enough proxies will behave well enough that at least the HTTP bit of the app has a chance of working.