African Soft Furs sizes

I’ve been breeding soft furs for about a year now. I was wondering if any other soft fur breeders have noticed a size difference between males and females.
My males can hit 75 to 90 grams 3 weeks after I put them in grow outside but my female barely break 50 grams even after a 4 month grow out.
The only time I see them put on any more size is after I’ve put them with a male.
Is this common?