Something that may be a factor here… When you are doing words you are free to combine those words in whatever way you want, you have the freedom to make them interact or merge or whatever your brain wants them to do in that snap read moment. Because you instinctively link them, I think it makes the recall easier.
With the arbitrary action in your PA, you can’t just use the first thing your brain WANTS to use to animate the scene. You are forced into imagining something that you didn’t actually come up with. If you aren’t 100% perfectly focused, and the scene is kind of meh, its really easy to lose it, almost like reading a paragraph when your attention wanders and immediately realizing that even though your brain maybe said the words you completely missed internalizing the actual content.
I think this is a weakness of card (and number) systems that use Actions.
If you had a Person/Object list, you might experience a more similar construction process to what you do in words. See the two things and make a snap connection. I know at this point you don’t want to mess with the system, but that may be a big cause for this issue.
You’re gonna love it.
The issue you may be experiencing due to actions goes away since most 2-card systems don’t pre-define actions. You’ll have the freedom to create like you do with words. Half the number of elements to represent a deck. Half the number of loci needed. Of course you’ll need to learn at least 1352 associations (or 2704 if you really want to go all in!) but given how tenacious and dedicated you are to this, I know you’ll be able to smartly tackle that workload.
What system are you considering?
May I suggest going for one that provides a built in 3-digit system as well so you can upgrade two events for the price of one? Where all the sounds are based on Major so there are no new phonetic associations to learn? With a fully consistent and simple way to translate every card pair? With zero ambiguity in how to read every suit combo and card value and 3-digit (and 2-digit) number? That can be built as a 2-block or as a full true 2704-pair system? If only there was a card and number system that did all of these things… Hmm… 