[Heaven's Night]

Something to take note of, boobs flattening out when raising arms, straightening back, pulling arms back etc., is also a characteristic of wide and or tall breast roots due to larger connecting surface area and lesser projection. But that doesn't make the breast "disappear", only to flatten out.

This is typical for anyone with wider chest or just genetics for a wide and tall breast root. I had a big struggle with this until I learned about how breast shapes work and what I have going on. And later told by my surgeon that this is a typical eastern Finnic genetic trait, very common around where I come from. 

Here's a some useful graphics to illustrate the most typical breast shapes.

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