I’ve found the answer as to why this was occuring and am now happily back to looking at a screen where the distance of all flights given in the data column correlates with the rings on the map.
Just in case anyone else encounters this problem, it occurred because I had inadvertently changed my Map Projection setting from Mercator to Cartesian.
You will see if you choose the Cartesian format,- having first turned the Mode-S Signal Maximum Range option on, and the Radar Rings option off, - and then click on the ‘Zoom min’ icon, that the map is projected from a point which shows the Max Range in the form of an ellipse. On the other two map formats it is circular.
Turn on the Radar Rings option and you will see they do not correspond, - they are circular, not elliptical. Hence the discrepency.
I suppose there must be a reason for giving users the choice of a Cartesian map but it would seem that nobody in the forum uses it or this problem would surely have come to light before.
Anyway, as the option is there, perhaps Development will correct this anomaly in v1.6 or at least inform users of it in the manual.
Hawkeye