Gaining

Depends:
- gender, height, build, amount of muscle
- previous stretching (weight gain and loss, pregnancy)
- carrying more fat in the abdominal cavity ( under the muscle, makes for the hard ball belly) vs under the skin (soft)
- where you carry your fat.

I'm 6'2" 380lbs and while it hangs a little while standing, it hardly hangs/sits into my lap when sitting.

I appear to have a long ways to go before I have a belly instead of a lap! lol

So it just happens. It's all how your body holds it/takes it.