Mark,
This has been discussed pretty in depth on bladeforums, so maybe that thread will help you out =)
Understanding what terms are being used helps a lot when discussing this topic… please refer to the charts here. I use the western understanding of the terminology whereas you will use the european terms (like Murray Carter).
So using the terms you are aquainted with, the thickness of the edge refers to the thickness at the “shoulders” of the edge, or in other words, the point at which the primary edge transitions into the secondary edge.
Where this becomes obscured is when you start talking about convex edges, which is why some people (like knifemaker Joe Calton) have advocated measuring at a certain depths into the blade to have a standardized way to tell cutting ability. So I would say that it would not be bad to measure at 5mm into the blade from the edge, I would also measure the transition point though.
Hope this helps!