There's no such thing as 'density of gravity'. Gravity isn't an object. And there's also no 'gravity around an object'. What I meant is, I think Chuuya can pick a point or a core where he exerts gravitational force. If he wants to stick to the ceiling, the small area of gravitational pull will be on the ceiling, keeping him up there as if he's standing on solid ground. Also, by manipulating the gravitational acceleration, he's changing the weight of a person or object.