For example, in HTTP(S), its response is always larger than the request, but the most common censorship-targeted information is the Host header and TLS SNI, all in the request. China has stopped filtering HTTP HTML responses since 2008.
But from this, different places may differ.
I agree that it’s non-standard. But the OP is asking if it’s possible, be able to or not, no?
No idea why it failed, as they said. The iatMode seems to not affect read/receive.