You either have to be very submissive or very dominant. I don't know exactly how high. But around 15 should be enough. Your sexual interests have to be pretty high (around 13) as well. Why? Because you will take the task of being breeded for tons of orcs and give birth to their sons.
Unfortunately, no matter what kind of sex you have with them or with how many, it's not reflected in your Sex Stats. Only the number of orc babies will be recorded.