Wouldn't the app registering the card provide the card image? And actually cards from the same provider/app are suppose to occupy the same "vertical" slot but then show a horizontal dialog. Also, I bet even with the identical looking 20px preview, the actual order is consistent so just remember which is which - same interface physical cards provide.

Is there a reason to not pick a single card as your default payment card? I find it's pretty rare I need to pick a card manually unless it's a store card or card for specific spending type (resturants, gas, etc.)