are you dumb?
I Didn't said that only her half body is effected by the gravity.
For example, IF you are a fat person and you're walking on the QuickSand then you will get pinned down in ground more quickly because of your big fat ass than the person who is less fatty.
Same goes for kaguya's dimension.She has immense amount of chakra that's why she got pinned down in the ground rather than lying on the ground too.
Please use your mind rather than ass

Naruto and Sasuke are lying on the ground just because they have less chakra than kaguya.IF they have the same amount of chakra as Kaguya then they would be pinned down in the ground U_U