Yup you got the reason exactly, going to stick to 3 ingredient combo's just to keep everything consistent.and how do you do it without making player feel like it's some bug because nothing happened after adding 3 ingredients? adding 3 with the current amount of ingredients available is already a ton of possible combinations, and most of them are still yet to be utilised, there's nowhere near a need to pack in additional ingredients to the combinations
That said void, regarding sex scenes with other characters and monsters, definitely happening soon. This update or next.