HBP/PE4 Shoulder Position

Today while doing my sets of bench dips I noticed that retracting my scapula near the top of the movement significantly increased the work my triceps had to do. I'm hesitant to do this consistently, however, because I recall, but of course cannot find, a post by Daniel or Josh mentioning protracting being desirable for some dip variations, but I may have that backwards. I've been looking over the course video for a few minutes now, but I'd like to get some of your opinions on this. 

Do your best to retract your scapula through out the range of motion.  You will need strong triceps for hollow back presses later.