@markmceachran – I’m viewing on a large, non-retina Mac monitor and I don’t see any image cropping at any viewport size (first time I’ve been able to say that about any full-width slider hitherto). I downloaded your images to be sure that none of the data is being cropped.
What I do see is scaling. With a responsive theme, the slider images obviously have to be scaled down in size so that they can be viewed on different devices. At their default size – 2000 x 500 – your images butt tightly up to the grey rule at the top only when the viewport is 2000px wide. As you reduce the viewport, the images become shallower – for example, when the viewport is 1000px wide, your images will be scaled to 1000 x 250.
In an ideal world (imho), the scaling would be done from the bottom of the image so that the top always stayed tight to the grey rule, while the rest of the page content moves up into the scaling-generated white space. But the algorithm is scaling from the middle with the result that white space is generated above and below the slider. Thus your slider effectively moves down the page, away from the grey rule, as it scales down below 2000px width. But the images remain complete and uncropped.