Hey guys, I was wondering if it's common for different bloodlines to be different sizes as adults?

I currently have 2 breeding pairs of rats. My BEW's which were purchased from a Mousery (large warehouse mousery) that breeds specifically feeders.
I also have a pair of high white Russian Blues which were purchased from a small rattery that breeders just for pet rats.

I noticed my BEW's were a bit bigger as adults than the other pair but I was really shocked of the size difference when I paired up the BEW male with the high white Russian Blues girls.

The female in the picture (the blue with her hands up on the water tube) is over 6 months old and (I believe) fully grown. The male is about 7 months. I know males tend to get a bit larger than females but he is almost twice her size. Is it common for different bloodlines to be this different in adult size?