And now back to the question of how Samus, a normally-proportioned human, fits into the shoulder and hip parts of the suit
It’s been like 20 years since I played it, but I seem to remember some logs in Prime referencing the horrific results of Space Pirates trying to replicate the morph ball.
I can’t say how logical it is, but lore-wise the suit doesn’t actually frame her body proportionately, it’s larger and her feet only go to the shins and her arms only go halfway down the suits arms. The way it moves without 1:1 mechanical input from her body is assumed to probably be related to the “biological” aspect of the suit inside that is made of living tissue and is essentially an extension of her nervous system. Also alien-bird-DNA
This also ties directly into the plot of Metroid Fusion, were her encounter with the X parasite caused the biological components of her suit to fuse with her body. In order to stabilize her, the alien-bird-dna already fused with her human dna was further fused with metroid dna. Fusion! Fusion! Fusion! Do you get the title yet? Fusion!
There was actually a really old Super Metroid magazine ad which featured a cutaway view of Samus inside the armor and it showed how she fit inside!