There was no need to switch that as that will have no effect on the group that your sovereign starts with... Here is a copy of the code from CoreUnits.xml under the "Sovereign_Relias". Notice the number 3 (you might want to change that to a higher number as well). You would need to do this for each of the sovereigns.
Also, if you are going this route, you will need to look in CoreWorld\CoreFormations.xml
as well. They only have arrangements of units up to 9. So you would need to add your own formations up to 20 people (add in 11 more formations, otherwise those units will never appear and you will get weird effects).
You will need to go through all the single spawned units, like trolls and dragons and beef up their attack / defense to account for the larger number of troops and the higher attacks. For example, when you have a group of 20 troops the damage is not a simple multiplication, but 20 different strikes are measured and so you would have to account for this damage increase.
The heroes under this system will be highly reduced in strength as well, unless you change them as well. But changing the equipment they use will be a rather daunting task, as you would have to make a hero copy of each item and a unit copy of each item, as one option. Otherwise any damage increase on weapons will also be visited by units. Unless of course you go through each hero and just give them a simple attack bonus (which means you would probably have to add attack bonuses the hero gets per level to account for the larger number of troops), not to mention a hp increase just to keep heroes in the game a feature.
Looks like you are going to go through a lot of work to get this to balance out, good luck.