Usual/Default Behaviour

If there are more than 6 lots available, images will display in order of lot (i.e. the first image for each lot will display) or if items are featured, their first image will appear first, as shown here: 


4 Lots, 1 Image per Lot

If there are less than lots all with only one image each, they will try to compensate for the extra space by appearing larger: 

In the image above, image for for item 4 appears larger to fill the space. 


4 Lots, Multiple Images 

If you have less that 6 lots but some have multiple images, the images will prioritise first by number and then by extra images, as follows: 

In the image above, the first image for each of the four items is displayed first, followed by the second image for each item that is available, then it would be the third image for each item, etc. 


4 Lots, Multiple Images, Featured Item

If you have less than 6 lots and have featured one lot, the images will prioritise first by featured, then by number, then by extra images, as follows: 

In the image above, lot 4 has been featured so it displays first followed by the first images for lots 1-3. Then the second image available for the lots displays, followed by image 3 for the lots, etc. 


Summary 

In summary, the preview images in the list view of the auction calendar are displayed differently depending on the number of lots, number of images for those lots and whether there are feature items. Lot order take priority unless there are any featured items. Feature item images take priority, followed by numerical order, followed by any additional images.