With regards to the above changes to try and get the theme to use smaller image sizes, can you think of any reason why it wouldn’t work on Macs with Retina displays?
We’ve looked at the site on a few different machines and the result always seem to be the same – on Macs with Retina screens the original full-sized images show, but on machines with non-retina displays the correct sizes show.
For example, on the home page, the images are the correct size on non-retina displays (they have 800×450 in the file name), but on Retina displays they are the original full images (and don’t have a size in the file name).
We’ve tried all the usual tricks – different browsers, and cleared the cache multiple times.
BTW, this relates to the same site as the original query – David is a colleague.
My GeneratePress-based portfolio: http://www.pauldixonwebdesign.co.uk