Hello,
I've never heard that the scorpions vary in size depending on where they are found in the docks. It would be interesting if they do in the tiny area they are found though.
I haven't actually been to Sheerness but I do have a few E. flavicaudis that were collected for me from there. Given the cold weather we have been having I doubt any would be active but I have heard of people still finding the odd one during the winter.
As for taking pictures of them, going by how mine act, I'd say they are one of the easiest species to photograph. If your very quiet, don't breathe on them and keep your movements slow they will normally sit perfectly still i.e. I'm not moving so you can't see me haha. If you were trying to manipulate them into a good pose for a photograph though, they will more than likely bolt for the nearest cover.
I love them, they are a really attractive little scorpion and are so mellow, I've never seen an adult use its sting. I'm desperate to go down to Sheerness and have a look for them but it's such a long drive for me.
I hope you get your pass into the docks. It would be great to see some pics of them in their (kind of) natural habitat.