Do you mean that a particular sex may be smaller than the other? Could you be more specific?If you want to try, you need some luck. Maybe, you can look at the body of all you have. You will see, that some have e smaller baddy like the other. This is maybe a different between male and female. So you put them together. Sometimes it will work, sometimes not.
Have many many luck at your breedingproject.
Regards
Andreas