Is it the light, or do you have a double bevel going there toward the heel?
You were indeed correct here - about the last cm at the heel isn't set. I assume something to do with the spine wear making the bevel angle lower, which seems like it may be a bit tricky to sort...(?)
Wouldn't be the end of the world I suppose, I don't tend to us that part of a razor very much. So if I left it blunt (rather than half sharp and tuggy) I doubt I'd notice.