Thanks Tectronus, I also have the correction mods added to adjust for the x6 scope that I am using. I get the correct range when I manually enter mast-height.
I am getting well used to manual input of mast-height so I am happy to continue getting the range this way.
It looks like I am the only one who gets this issue. I am sure this is my fault as I have been careless with mixing and matching mods. Every time a new on comes out I have to try it. (not always in port either

)
I have nearly reached the end anyway, when I do I think my best plan would be a fresh install. (I have also tried the fix for mod soup)