The difference between the two contending armies is an even 20,000. While it is quite likely that the attacking army had the superior troop strength, the fact of the difference being expressed in this type of a number suggests symbolic differences rather than counts. This also follows from the difficulty of obtaining any kind of accurate count of one’s enemy.
It is interesting to note that Mormon is fighting with depleted forces, while the Lamanite/Gadiantons are fighting with replenished forces. That last troop-strength numbers we have came in the land of Joshua at the beginning of this sequence. At that time, Mormon gave his own troop strength at forty two thousand and the enemy’s as forty four thousand (see Mormon 2:6-9). Even though those are also likely military units, it is clear that there is a difference in the trend in numbers.
The Lamanite/Gadianton robbers are getting larger, and the Nephite troop numbers are smaller. The reduction in numbers tells us again that the Nephites have been engaging the Lamanite/Gadiantons during this flight, accounting for the loss of numbers. During that same time it is certain that the Lamanite/Gadiantons also lost men to death and injury. However, they are receiving reinforcements either from their homeland, or from those who had rebelled in the land (Mormon 2:8).