I don't believe it is product specific, rather it depends on the size/res of your uploaded image and how the program might need to scale it to fit your design choices. I just tried it on a door mat in default horizontal position. My image on upload was apparently fine for that so I switched to vertical orientation (my image was a tall skinny one) and then chose Fill and then yep, got the prompt about Enhancing. Then I tried a medium gift bag with a small square image. No prompt to Enhance until I clicked Fill which of course is going to be making the image larger. For me though, if I make the image larger than it should be I first get the old-fashioned yellow warning symbol, then it takes a couple seconds for that yellow warning to change into the blue star symbol with text tip that says something like 'please wait, we are upscaling your image' and then you get the screen that says it's done and to preview original vs upscaled. So if you think the image is too small, you might need to give it a minute to sense it needs upscaling and do its thing.
I don't think there is a manual option to choose to upscale something, it just appears and upscales automatically when it senses your image isn't large enough for however large you made it.
Also FYI - noticed in doing this tonight that the upscaled version of the image that gets added to your image gallery no longer has a long name of random characters, instead it gets the exact same name as the original image. UGHHH!! It does have the blue star icon on it whether viewing from My Images or while viewing Uploads when in the Design Tool, but it would be great if they added _upscaled to the file name.
