multisite mapped domain image url?

Hi, editing the meta data on images shows that the image url is set to sub domain and not mapped domain

ie

subsite.maindomain.com/wp-content/uploads/sites/10/image.jpg

is this correct?

would have thought it should be

mappeddomain.com/wp-content/uploads/sites/10/image.jpg

does having path set to sub domain affect google ranking?

thanks