I'm assuming you are reducing the size of the thumbnails to small using the S button on the bottom left S/M/L buttons to get more on the screen.
I'm also assuming that you know: holding left mouse button and dragging moves and image, holding right mouse button and dragging swaps two images. This can make things a little easier.
We will look at this in the next version and see what can be done. Automatically scrolling down when the mouse moves above or below the images would seem a good idea. It may able be possible to offer a pop up window that can be resized.
Out of interest how many images are you working with?