When a skybox is used, the level is enclosed in a cube and we can see the "sky" on it. The textures for skyboxes used in both KotOR and TSL are square and one really utilize 5 out of the 6 sides, the four sides and the "ceiling." Standard floor textures would make the 6th texture pointless.
not to scale However, as it appears that for the Malachor V skybox, the sides aren't equal. not to scale At least one of the cube's sides is more like a rectangle. This means that the texture for one side won't match up to the edges of the other. My question - is actual shape of the invisible skybox framework hard coded or can it be adjusted via modding?