A to B 1
A to C 2
则，为符合等比例原则：
B to A 100
C to A 200
若
A to B 1 B to A 100
A to C 2 C to A 30
则
流动失衡
导致
A to B 1 B to A 15
A to C 2 C to A 30
A需维持空间规则
否则A的生产线会崩溃