OK brains trust, what am I missing here...
Went to move my scope from one rifle to another. Found the bell end was touching the rail. No problems, checked the Leupold site and from the old packaging that I was running a MEDIUM height in 34mm tube diameter. The site says HIGH is 29.7mm in height, so I figure given Medium is 21.6mm the extra 8mm would be heaps. Is measured from base to centre line of tube.
I was surprised to find the High one made very little difference. So I started measuring the differences and the Medium to me seems a lot closer to 25mm or something. Which has me stumped how can it be out by so much. I just can't see anywhere the 8mm difference.