Reason for this is because its unclear if you are sleeping next to your partner and spooning or full on smashing eachother.
You have an option (can select it on a bed just like you would doing a sandman kill)
Having actual six gives you the normal lovers embrace perk but adds +1 char (cause ur relaxed and feel great in life)
Sound effects could just be the occasional grunt they make in combat..not the really painful sounding grunts though cause like if ur doing a girl it will seem like your going for anol all the time without lube..apocalypse or not that aint realistic!! Haha