If-Modified-Since

Hello! My WP don’t send answer “If-Modified-Since” and 304 response for unmodified pages. I have special plugin for it and W3T have to do it. I think we need some options in nginx config file. Ive checked by http://last-modified.com/ and there is some information, why everyone need it. In nginx docs some commands about that - http://nginx.org/en/docs/http/ngx_http_core_module.html#if_modified_since, but I don’t know to use them.

Anyone have resolve this problem? I think EE must support it by default.