Are multiple fills on a team random?

Recently my friends and I have been all selecting fill when we have a group of 5 and want to have a bit of fun playing normals, but it seems like we all get the same position every time. We were under the assumption that it would assign the roles randomly, but it appears not to be the case. We have even started making new games instead of clicking play again to see if that changed anything but it didn't appear to. Are we just randomly getting the same spots over and over, or is there some method to the madness? I was just wondering if anyone had any insight to how it worked or had similar experiences.