I don't know why they would weight it differently. It's an academic reference non? They might say that the person hasn't known your that long (only a semester) but perhaps the prof could mention in their rec that despite you only being at UNSW for a semester, you made the most of your time and developed a strong relationship immediately, etc. etc. Get the people who know you the best and can speak to your abilities the best, if that's an abroad prof. get them!