Okay I’ve been drawing manga forever and I just gotta say you are really good. If you are looking for ideas to improve i’d say the face area Like you said your heads are a bit big but that isn’t really a problem if your eyes are larger. My favourite thing about drawing manga is the eyes the more detailed and more light bubbles the better most of the time in my mind. I noticed your hair is often very triangular which may contribute to the face perspective softer more natural hair may work better. I tend to go almost to realistic on my manga bodies so I’m not really the best to ask on that account.
I wanted to say Woah! to the clothes on your sketches they are amazing!