Synthetic Monitoring using proxy servers

Hi, elastic staffs.

I have two questions about Synthetic installed in private network.
It can not call any outbound requests to the internet unless I do any network works.

  1. I read the heartbeat document below about synthetic options.
    Browser options | Heartbeat Reference [7.14] | Elastic
    But, I didn't find the proxy_url option. Other types like http, tcp have the option that calls the proxy url instead of hosts.
    Can I apply the proxy_url option when using a browser type option?

  2. As I said earlier, It can't call outbound requests to the internet now.
    When the synthetic monitoring agent call the url, it gets network timeout 30s.
    But, it judges "Up" count even though the request fails because of the network block.
    I want to know that the way to judge "Down" when I get the network timeout.

Thank you in advance!!