Another thing I found difficult about backing the 2nd to 4th favs on the TAB is the constant change in prices. You can try to wait till the last possible moment, but in some races, your bound to end up with one of your selections being displaced in the top 4 by another horse right at the last moment. Or possibly the horse which is 2nd favourite when you put your bet on, comes in late in the betting and becomes fav.