Unfortunately some families did move around. Suggest you find out if there is a marine or farming or mining background within the group you are looking for.
Most of the Metherell farmers stayed close to the North Coast but covered both Cornwall and Devon. If mining by 1730 the Cornish mines had a plip and later on the Tamar Valley came on strong on both sides of the Tamar. Maritime folk out of a number of places like Bude, Hartland, Clovelly, Northam, Bideford, Barnstaple. These places had trade all along the English Coast and Wales through to Ireland and Newfoundland, USA and beyond.
Does the group you are searching for has any trade or services connection.