My GGGgrandfather William Sibbald (b 1789 Kinghorn Fife) was a physician and Assistant Inspector (AIH) in Ceylon. He was there with his wife Euphemia (nee Wright b 1790 Oporto)and daughter Jane (b 1823 in Mauritius - on the way there or back?) from before 1823 to after 1832. There is a brief mention of him in Johnston/Anderson's "Roll of commissioned officers in the Medical service of the British army". Do you have any more information about this family when in Ceylon by any chance?
We don't know which regiment he was with, nor where stationed.