It should work exactly how you explained it. We tested the functionality and it is working for us.
Check the following in the Pricing menu:
– Width and height for the image size is correct.
– Update the image sizes by clicking “Update” in the “image sizes” table.
– Delete the the image size from the price list and add it back again.
This will ensure that all that is up to date just incase something is corrupted.
If you are still having issues can you prove a example download link