> And you are reporting that it does not ever write to "ssd_cache".
Yes, this is correct. I want to choose the cache location based on the size of the cached file

I want to get the behavior described in the article, but only with the file size in the map directive, I assume I need $sent_http_content_length or $upstream_http_content_length.

https://www.nginx.com/blog/cache-placement-strategies-nginx-plus/