The balance plugs are connected to the parallel board. Lets call batteries A, B, C, D. Then let's call the cells 1,2,3,4. So A1, B1, C1, D1 will all receive the same voltage. The lower discharged batteries will take more current until the A1, B1, C1, D1 reach the same voltage. Then they will charge roughly equally until they reach 4.2V. Balancing is charging each cell to an equal voltage, which will be achieved. But the lower cells will receive current above 1C in the beginning. Once voltage of A1=B1=C1=D1, they will draw the same current until they reach 4.2V.