Thanks Maxim. Is it possible the filter on a value "larger than" or "smaller than"? How would the regex in the map block look like? e.g. smaller than 1000000?

I tried something like this, which is not working:
map $upstream_http_content_length $docache {
default 0;
"~*([1-9][0-9]{0,6}|1000)$" 1;
}