Thanks guys. I suspected as much. The material is DOW blue foam, so very easy to cut, but not very stiff, and it flops about a bit. In case you’re wondering, it will be covered with carbon fibre. I don’t have a table saw, unfortunately.
Jeff, you mentioned a stl file, which would allow the router to carve away the offending wedge - how does this work? If I used very small incremented passes, there wouldn’t be a lot of tidy up work to do. I’m going to go in search of stl-type instruction on the web, but please feel free to suggest an approach which would work.