I think you are right, BUT nowadays just how many voters in Cornwall are concerned with 'Cornish' issues, by which I mean issues such as farming, fishing, second-home ownership/housing, economic support/development (be it from the EU» or Westminster...) is something I am not so sure about. Just 10% of the population identified as 'Cornish' on the 2011 census. I wonder whether the remainder are 'Kernocentric' or 'Anglocentric' or 'Britocentric' in their views - or even if a geographical/ethnic identity' filter comes into play at all.
The census form does not have a tick box for Cornish - it has to be written in on the box for other.
There has been a long running campaign to make it a choice tick box, but Westminster appear to not want to recognise Cornwall's constitutional status as a Duchy or it's inhabitants as Cornish, in spite of Cornish being recognised as a national minority