The pectoral muscles are originally divided into two parts: upper and lower pectoral muscles, so it is not difficult to understand that it is necessary to practice flat and upward inclined bench press in normal training. The layering you are talking about should be the dividing line between the upper chest and the lower chest. Many bodybuilders can see the dividing line. Some enthusiasts can't see it all their lives, hehe, everyone's muscle shape is different. It is normal to rule out the possibility of deformation after injury, as long as it doesn't hurt.

As for the solution you mentioned, because one side of everyone's body is habitual (right hand or left hand), it will lead to uneven exertion, especially when doing barbell bench press or push-ups, the habitual side will give priority to exertion, so it is not difficult to understand why one side is big and the other side is small. Hehe, I personally suggest using dumbbell bench press instead of barbell bench press.