I think this is just a problem with current Poser characters that we have to learn to live with. I usually end up touching up the elbows and knees in postwork, some characters are better than others in this respect, I find the P4 characters quite bad, "Latexa V2" to be the best of my characters, with Victoria 2 somewhere in-between. Unfortunately Latexa V2 was no longer available for download the last time I looked.

Playing with the joints in the Joint Editor has possibilities, but I don't have the experience to give advice in that field.