Though the structure of the carport benefits all four proprietors, the placement of the one supporting pole would be of benefit of one, being the one on the end, if moving this post allows easier entry/egress to their parking space.
If the post is not moved so that it is over common property, does it still allow the owner access, albeit difficult access? Then again, if the post is within the car space and not offset and the owner knocks and damages it whilst attempting to park, then it would be the OC that has to wear the cost!
Though not familiar with the licence approach, it would seem to me that this placement may well have to be on the shoulders of the one owner if they want easy access and if the OC is to be protected in the future!