No rules, just physics.
It is about leverage. The angle where your sting meets the bow is almost 90 degrees. Pull the bow to about 20 inches and you will see that the angle is a lot smaller, maybe 60 degrees. The closer a bow gets to 90* the harder it is to pull. How hard it is to pull is a symptom of "stacking". A lot of energy that you are putting into the bow is being wasted and will not be transferred to the arrow. If you get beyond 90* you risk the string popping off, and get really low energy return. Recurving, or in this case flipping the tips reduces the string angle and makes leverage work for you making it easier to draw and putting more of the energy you used to draw the bow back into the arrow on release. On longer bows, the string angle doesn't get near to 90 so they draw easier. On short bows, you have to be careful of this.
I thought the same thing Gordon. The string angles seem really high for that draw length and that length of bow.