This business of 'brake shoes' is tricky. I've seen many combinations over the years.
Primary and Secondary shoes are normally identified by 'PRI' or 'SEC' but not always Some are made of different materials (hardness) which are different in color. Some are longer than the other but not always.
The front shoe requires less pressure, to produce the same braking power as the rear. In other words, the drum rotation 'helps apply' pressure to the front shoe. The easiest way I can explain this is by citing hand brakes on a bicycle or motorcycle. A light pressure on the front brake does far more braking then a lot of pressure on the rear brake.
Bottom line: This is a system that brake companies engineered to balance braking power. Shoes MUST be installed correctly according to the Shop Manual and the manufacturer's instructions.
BTW, my personal preference is, bonded brakes. I've always had good luck with them but I 'stay on top' of the lining or pad wear. I also choose the softest material I can find. It wears out faster but also stops easier without chatter. - Dave