The default positioning for the grid is automatic, which is similar to static. Meaning that it follows the natural document flow. From top left to bottom right. You can change that behavior by changing from automatic to manual to the cells of your choice. There’s a lot of flexibility.
For the most part, you should be able to add items to your collection and it will follow the grid settings, so you may need to readjust and you may not need to.
Someone with more expertise might be able to parachute in as I have not built a site using collections the way you are. I’m just trying to give you food for thought in hopes help you grasp how “Grid 2.0” works. It’s really great.