I am pretty sure I figured out how it works. And it definitely helps understand why you can get all four prey mods to be the same so many times in a row. I seemed to have noticed that every time friction fire came up the other three mods were the same. same thing for the grenade launcher, same thing for the linear fusion rifle. So I think there are only three or four different combinations of prey mods that will come up each time. so instead of randomizing a whole bunch of different combinations it’s just a handful. That makes it more plausible that you get the exact same four. so many times in a row. One and four versus one in a multiple of four. They probably had to do this so that you would get four different mods every time. If it was 100% random for all four mods then in theory you could get the same mods in all four slots and they are probably trying to prevent that