Rpg Maker Developers Group

I'm not entirely sure if this is the right board to post on because the question I have is regarding the editing of the .yaml files. I'm now finally getting the hang of Luna Engine, but I've reached the limits of what video tutorials and documentation can teach me (unless there's a great tutorial I've missed.). My game is an adventure-puzzle game, not a combat RPG, so I'd like to have a minimalist UI that gives plenty of info with minimal design. However, since it's not a big UI, what I wanted to do is have it pop up under the player.

What I thought about doing was setting two RPGMV X, Y variables that read the players Screen X, Y then using that as the values in the .yaml file. Seems like it would work. Problem is that I don't really know how. I've made puzzles before that require an object to be an X, Y in order for something to happen, but this seems like a different beast.
What's the JS code I'd need to enter here for the .yaml?