it is possible that the Riding officer came from Co Down - as I suggested at that time the posts were unlikely to go to a manxman.
The first birth in IGI is dated 1779 with a death (or Robert ) noted in 1780 - on second thoughts this may well be his son (eldest ?) so looks as if they arrived on Island c.1779 (he was noted as formerly Port Gauger and Deputy Controller in the port of Douglas )