Flipnote space and how it works can be somewhat obscure. I did some testing and here's what i found about it. There's some stuff missing here. For example if there's similar images (pixel coordinate-wise) in a row that's only saved once and it saves space. If you copy and paste something to an empty layer and move it,
I did tests in the past and came to a similar conclusion, thanks for sharing this info for others to learn you did a great job!