In 2013 someone paid Aecom, a major international consultancy firm, to do a major study piece on suitable locations off road for lorry parks on both the A2/M2 and A20/M20 corridors. Cox Hill was one of many, many sites investigated in that study and was ranked as the second choice on the A2/M2 corridor. Exactly why it ranked so high is unclear to me - I know the area and the junction well, the topography is a long way from being ideal (not as flat as the report indicates), too many houses too close by and downwind of the proposed site and the junction and road alignment would require significant re-engineering. There are better sites off the A2, one of which is not a long way back up the road towards Canterbury, does not interfere with existing junctions, has minimal nearby housing, and upwind, and benefits from much flatter topography.
https://democracy.kent.gov.uk/documents/s49183/Aecom%20Final%20Draft%20Report%20-%20Site%20Assessment%20-%20Appendix%203.pdf