Thanks again for all your replies and links from Jerry, really helpful.
John, I haven't actually tested the results with the invercone, just the baffle open and closed. I might do that.
Richard, zero-ing is spot on in both modes. I hadn't considered being inside affecting the results. I will try outside and see what happens.
Interestingly, I too have always had well exposed negatives using the meter. Maybe my OCD is just getting carried away
Thanks again