I too have a Masterman of Dorset connection, however, it is a bit further back; Elizabeth Masterman (1683 to 1741) who married William Taunton. She is probably the daughter of William Masterman of Winterborne Whitechurch, Dorset.

I was also looking to see if there was a connection to Nanny Masterman, mother of Thomas Masterman Hardy of HMS Victory fame. Nothing so far.