Just to add my 2 cents.
I emailed HQ with a description of my face and they said mystery cache is fine
My idea the user doesn't have to go further than 150m from the start in a open field to unlock the cache (gps tool in the physical cache with a distance indicator)
So they said it's allowed.
I think what isn't allowed is taking the cache far away (multicache style) so if someone else comes along there is no cache or no person visible
Where as my idea it's in a open field so all line of sight