Concerning the following pages:
https://confluence.atlassian.com/doc/running-confluence-behind-nginx-with-ssl-858772080.html
and
https://confluence.atlassian.com/confkb/how-to-use-nginx-to-proxy-requests-for-confluence-313459790.html

It would be incredibly helpful to see the client_max_body_size directive added to both the /confluence and /synchrony location blocks with some clarifying comments.

Context:
The default value for client_max_body_size in nginx is 1MB:
http://nginx.org/en/docs/http/ngx_http_core_module.html#client_max_body_size

In the /confluence location block, this value should directly correlate to the "Attachment Maximum Size" under "General Configuration" and should be noted as such in the aforementioned documentation.  A client_max_body_size lower than the "Attachment Maximum Size" will cause HTTP 413 errors ("Request Entity Too Large") when uploading attachments that exceed the client_max_body_size.  Matching these values will allow Confluence to display a more user-friendly error if the attachment is too large: "{attachment-name} is too big to upload. Files must be less than {attachment-maximum-size} MB."

In the /synchrony location block, the default 1MB value is too small for editing certain page sizes in versions 6.0+.  This will result in HTTP 413 errors in the browser console when attempting to edit the page while the UI displays the "Loading the editor's taking longer than usual..." error message but will never proceed.  Adding the client_max_body_size directive with a slightly higher value here can resolve issues with editing larger pages.

I know Atlassian's philosophy is that reverse proxies are allowed but the support team does not provide assistance for configuring them.  If documentation is already supplied to the current detail, it may make sense to add these fundamental directives to the sample configuration with some helpful comments.  This would enable admins to proactively prevent inconsistent attachment upload and Synchrony editor loading errors if they are following that documentation to the letter, as I myself had done.