Действительно, ошибся, когда пробовал host: и Host: - думал в этом дело.
Но с правильным форматом тоже не детектит
telnet 104.16.120.110 80
Trying 104.16.120.110...
Connected to 104.16.120.110.
Escape character is '^]'.
GET / HTTP/1.1
User-Agent: curl/7.38.0
Host: www.bet-52.com
Accept: */*
HTTP/1.1 200 OK
Date: Wed, 07 Feb 2018 09:43:49 GMT
Content-Type: text/html; charset=UTF-8
Transfer-Encoding: chunked
Connection: keep-alive
Set-Cookie: __cfduid=dc1159d84c71b6d9aedabb9e18b10e3441517996629; expires=Thu, 07-Feb-19 09:43:49 GMT; path=/; domain=.bet-52.com; HttpOnly
Last-Modified: Fri, 01 Dec 2017 06:12:26 GMT
Vary: Accept-Encoding
Expires: Wed, 07 Feb 2018 09:44:49 GMT
Cache-Control: max-age=60
Set-Cookie: SERVERID=s2; path=/
Server: cloudflare
CF-RAY: 3e95682821d79041-DME