This totally makes sense. I understand why you did what you did and how this puzzle works. I find that when I have more open available space, that's when I run into trouble. Where do I put two shapes on a grid of 4x4? When people are saying it doesn't matter where these shapes go as long as the correct number of squares are utilized, then where do they go in the scheme of things?
usually it does matter where they go in the sense that there's usually only one solution. The way in which it doesn't matter is that if you can fit them into the same area you can have them in any valid combination and if it's (2x2 square) and (2x1 line) next to each other, the solution can be (2x3 rectangle) where you'd visualize it such that one of those pieces is not touching it's origin square if you get what I mean. And just because there are two Tetris pieces doesn't mean they always connect. Just usually.