The NPH feature will be supported in next release.
We buffer the response for the following reasons, to determine whether to compress the response, to maximize the compression ratio, to avoid TCP packet fragmentations, etc. And, if the response fragment is big enough, it will be sent to client immediately. In some cases, unbuffered might be preferred.
However, the log shows that the output is still buffered on the fast CGI side.
Thank you for the detail explanation. :-)