Calculate Current in Parallel Battery
By symmetry, the current through each cell is the same at 20/12 = 1.66A per cell.
There would be no current through the lateral connections (assuming all cells are matched).
The current through each of the lengthwise connections would be the same and each would contribute half of the current.
The current through each successive leg of the interconnect would go down by 1.66A as it goes past each cell. That is ~8.33A after the first cell, ~6.67A after the first two cells down to 1.67A for the last link.
Assuming the connections on the bottom are the same the current pattern would be the same although starting from the opposite end.
It is significant that the black wire connects to the opposite end of the pack from the red wire, if it didn't the connections would not be symmetric and there would be higher currents through the cells near the wire connections.
Additional lateral connections wouldn't help but adding extra thickness of conductor in the lengthwise direction would.