When Ordering Prints or layouts, if you have more than size for that item setup in your price list then the following controls which of those sizes will be selected as the default size when you first open the Place Order window.

1. If you are ordering a Print, it will choose the size that you last displayed the image at in Select Size View (in Working with Images) or in a Room (in Working with Rooms). If not displayed at a particular size before ordering, it defaults to the size set in the Preferences -> Display -> Calibration & Options -> Print Sizing -> Starting Size.

2. When ordering a layout, if you have set up the associated template in multiple sizes in your price list, it will choose the last size that you last displayed it at in Select Size View (in Working with Layouts) or in a Room (in Working with Rooms) or, if not displayed, the closest size to your original template's design size.

 If you have other sizes setup in your price list, you can just select a different size from the dropdown menu before adding the item to the shopping cart.