Also work around for cloth with 1 side face how i did it:
~ Bake scene with gpu lightmass.
~ convert back to cpu.
~ select the cloths and set lighting channel 1 or 2 beside 0, 0 is main scene.
~ make a new map and add it in the level context and setup simple lighting scene close to your scene, all light source for the cloth must be in the same light channel as cloths.
~ bake and adjust light intensity until its satisfying.