Shulchan Arukh Orach Chayim · Siman 627

English

The Laws of Sitting in the Sukkah, 4 Seifim: (One must sit in the air of the sukkah) One who sits under a bed in the sukkah - if it is higher than 10 tefachim he has not fulfilled his obligation.

English

One who sleeps under a slanting canopy that surrounds a bed in a sukkah - if it is not higher than 10 tefachim or if it has no roof the width of a tefach, he has fulfilled his obligation.

English

Regarding the polls which come out of the four bedposts, it is forbidden to spread out a sheet over them and to sleep under them, even if they are not higher than ten (tefachim). However, if one of them exits in the middle of the bed at the head, and the second from the middle of the foot of the bed (See Sukkah 10a) and a sharp incline is made from this side and that side, it is permitted to spread out a sheet over it to sleep under it because it has no roof the width of a handbreath above it. This is so as long as it is not higher than ten tefachim. There are those who declare this valid even if it is greater than ten tefachim.

English

One may hang sheets (or fabric) under the s'chach for ornamentation; if it is under four tefachim from the roof, it is valid. If it is farther than four tefachim from the roof, it is invalid. And if it is not for ornamentation, even though it is within four tefachim, it is invalid. (and there are those who take precautions not to hang decorations for the sukkah unless it is less than four tefachim) (Maharil)