Is a Matrix item treated any differently for SCA in terms of the item image naming convention or placement?

As many other properties (like URL), images go on the parent

Right, the tab isn't even present on the child items

the image naming convention should take care of associating the expected image (when you configure it correctly). But it doesn’t have to be a 1to1 relationship. Imagine for example T-shirts… You want images for colors, but most likely not for sizes.

I'm just looking to have a single image for all options. Do I need to name the files for the child items?

nope yo don’t even need to upload multiple images

So does it sounds like I've done everything correctly? It's still not showing

make sure your image separators are using the correct character

It's in the same format as our other items. I checked the config and don't see where the separators are setup, are they configurable?

Setup -> SuiteCommerce Advanced -> Set Up Web Site -> Edit -> Images -> Image Filename Format