That helps. You need to think about and share how you want the space to work.
It looks like your current setup is a dream as far as access. Easy access, top, bottom, all sides. It solves every problem we all hate as far as getting around the plants.
But as you say it does not max them out.
1st...grow style, veg length and your ability to SCROG should make it so each plant is 8oz dry harvest roughly (some more, some less). If they aren't, you have room to improve the veg part of your growing.
2nd...you need to redesign the 12x12 space to fit more plants and still allow good access. Are you considering a separate veg area or one big room that goes full cycle? If one big room, it's just a matter of layout. If you have a light meter, you should spend some time measuring your current layout.
Because you put the 4 fixtures right next to each other, there are much brighter spots and hotter spots where the lights meet, especially the center area.
My first goal would be to understand at your growing height how wide each lights quality growing perimeter is. And space the lights out to make one much bigger growing area or a few separate ones. Likely either a big grow space in the middle, more square shaped, or 2 rows of growing that are not linked for light. It really depends how you want to access it and how easy access should be.
