This XComMissions.ini adjusts the number of enemies spawned within each pod by one (except in some cases where lonely units are being given the company of two more units). As such it is not compatible with any tweaks that touch the very same file. 

For the Alien Hunters Version... please wait. There are sadly quite some complications and I invite anyone able to make a (working) version ASAP. 

Most notably, I do not have the DLC yet and I am afraid that the method I used may not work for since seemingly the DLC .ini acts like a Mod. 

Now, what were the criteria which decide which enemy got added?
Well, currently the arguably weakest unit of a possible Encounter got a copy. This is subject to change and requires more testing. It is likely that in the future other support units will be used instead (Most likely not Advent troops since there are plenty already and boss type enemies may be overkill...). 

It is worth to mention that the Number of pods is unaffected.
And obviously, more corpses mean more to sell. Balance is a very complex thing and this tweak is but one step to make this grand game more grand (and more fun in one way and another).

The Plus Version contains even more enemies. 
Notable changes: 
-Many Enemy Pods with the size of three, in IESS, have been eliminated and quite all 4-sized pods of IESS have been upgraded to 5. (=>at least two more than vanilla) 
-Pods with the size of 5 and above were not modified further. (=>still one more enemy than vanilla) 
-Additionally there is no limiton the number of enemies that can engage you, prepare to be overrun if you are not wary. 
-Handpicked some spawns for more variety and possibly danger. 
 
Changes range from 
"ConfigurableEncounters=(EncounterID="ADVx2_Standard", [...]" up to and including the line "ConfigurableEncounters=(EncounterID="Blacksite_FillPatrol",  [...]"

Installation:
0. Backup your XComMissions.ini, if you want to. Close XCOM 2, you have to.
1. Download the XComMissions.7z and unzip.
2. Move the .ini file into \Documents\My Games\XCOM2\XComGame\Config (default dir) and choose to replace.

In case it is not working, you might need to make the files read-only.

How to uninstall.
a) Replace XComMissions.ini with the one you backed up
b) Delete XComMissions.ini and start the game

Any feedback and bug reports are appreciated. I tested and proof-read this and am certain that there should be no bugs but it's not like I know how to summon enemy pods to check... Suggestions regarding balance are welcome, too!

Further recommended tweaks (recommended by yours truly so take it with a grain of salt) to accompany this one, some however may or may not be possible. (Links will follow when those are stable/exist in the first place)
-increased the squad size (however those are currently rather bugged and only allow 6+randomly selected units), recommended final squad size: 8 soldiers
-increased explosion radius for grenades (like in this case, one more integer can make a significant difference), recommended: +1 radius (can be found under optional files)
-increased turn limit for certain missions, recommended: +2 turns
-increased loot (Loot! Loot! Since more squad members also need more toys to fight more enemies to get more loot for more squad members [...]), recommended: +1 timed loot per mission (can be found under optional files)
-bigger backpack (one slot for utility really ain't much...), recommended: +1 slots (not that I know how, tried in vain...)
-"smarter" AI, recommended: More defensive, don't move for the sake of moving, higher fallback chance. (can be found under optional files)


Another Disclaimer: Since it's not like you'll suddenly face hordes of undead/aliens and as such there is not really a suitable screenshot or artwork for visual presentation, all I could offer would be the name of the tweak in Comic Sans. Oh and by the by, also imagine a Viper saying "Yes!" and there we go: An arbitrary abbreviation we can remember this tweak by.