But I can't post the line above with double "//" instead of just one "/". Cloudflare 
I think this is called the Browser Integrity Check, where the weird activity of any bad IP TOR as example that is trying to access */admin.php is checked, or sometimes some usual activity of bots or spammers, so PM them about this problem, or host the code in an external host and copy Link or screenshot.https://developers.cloudflare.com/waf/tools/browser-integrity-check/
This description is more accurate, as other than the CAPTCHA problem, which can be bypassed using code, I have not had any problems with Tor.
I read link you mentioned, but it said "looks for common HTTP headers" though. AFAIK our post data is send through something called HTTP body.
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I don't know the solution will work for you or not but I have done that on Tor in past when the website wasn't accessible due to cloudflare's issue. I have basically forced Tor to use France based IP addresses and the site worked well with France based IP's for me. I then created a topic to share the whole thing so that someone else using Tor may get help by applying the settings that worked for me. Here's the link of the thread: https://bitcointalk.org/index.php?topic=5459254.msg62527806#msg62527806
Does country of the IP address matter here? CloudFlare can easily detect whether you use Tor or not through many means (such as list about IP of Tor exit node).