I wonder if it is not so forthcoming?
Whilst Diapason definitely got the correct church (as is the point of 'Guess the Place'), so I'm more than willing to let him take the reigns.
However, the significance of the Romney Marsh sight line (extending from adjacent to Ruckinge churchyard to the coast just south of Dymchurch) of the Greenwich - Paris survey was that it subsequently went on to form the primary base line for the initial triangle upon which all other triangulations were taken. It was these triangles, extending from designated point to points (known as triganomical points (trig points to those familiar to mapping), which enabled the first accurately mapped survey of the entire United Kingdom to be produced. Though all the legwork was undertaken by Major-General William Roy, he died (1st July 1790) before the completion of the mapping had occurred under artillery officer William Mudge. It was his final maps that became known as the real 1st Edition Ordnance survey (known as the Mugde Maps) with Kent being produced in 1801.
Over to you Diapason