I am shopping for a scope for a 308 Norma Mag and yesterday at one of SA's premier gun & hunting shows I had the chance to view a lot of different makes within a short time & similar circumstances.

My first choice would be the Z5 3,5 - 18 Swarovski, but at nearly double the price of other brands it was prudent to check through everything. I soon discounted the Nikons & Zeiss options simply because I disliked the reticles available.

Leupold are the "go-to" option given their quality/price/wide range and I spent a lot of time with their VX3 4,5 TO 14 x 40 LR. It was mounted on a dummy stock and easy to ajust eye relief to suit.

I noticed a very pronounced difference in eye relief between the lowest and highest magnification setting!

The dealer, a good aquaintance and knowledgable hunter, could not notice it. I did not want to push the issue in his crowded stand, which was outdoors so viewing was good, but felt he was also adjusting his head a touch between the two extreme settings.

In my case it felt like there was at least 20mm of variance, perhaps even a full inch...

Has anyone else any knowledge to share in this regard?

I don't think you were seeing things. Leupold shows their VX3 4.5-14x40 as having an eye relief range of 4.6 on low mag to 3.8 on highest mag. That is almost exactly the 20 mm you mentioned.

My experience concurs with Gato. I think all scopes have this variance but Leupolds seem to have a more pronounced effect. They tend to have more and less critical eye relief than other brands and this is part of the trade-off. Despite this I still use them.

Correct, the Leupold variables have the center of eye relief about 4/5 inch different from high to low power range. However, they also have a longer window of acceptable eye distance than most other makes. This is an unavoidable optical trade-off. Leupold choses to make the eye relief variable but give it a lot of latitude, while some competing brands make eye relief constant but quite narrow. You pay your money and take your choice.