On the one hand, vanilla XCOM2 has enemies try to engage at very close quarters. On the other hand, it has enemies not get any range modifiers at all. So a shot from 20 tiles away will have the same chance to hit as the same shot from 3 tiles away. Needless to say, this is quite unrealistic. The close engagement ranges the enemies try to go for are massively advantageous for the player, since he does indeed get bonus aim for coming close.
A Better ADVENT changes all of these parameters related to range.
New ideal ranges
The “ideal range” is the number of tiles the enemies want to have between them and the player. If it’s more or less, they will want to get closer or further away until they are at the ideal range again. This plays into the evaluation for movement as part of the enemy AI, where all tiles in range are assigned a value for the unit and it will then go to the most valuable. In vanilla XCOM, the ideal range is 6 tiles for most enemies. A few of them have an ideal range of 8 tiles, which is still quite close.
A Better ADVENT increases these ideal ranges considerably, to a range of 8 to 12 tiles, depending on the unit.
Weapon range modifiers
As mentioned, the enemy gets neither bonuses or penalties for weapon range in the unmodded game. If the goal of the mod is increasing tactical play, this sort of thing can’t stay as it is. Almost all enemies use the same range table, which with A Better ADVENT now looks like this:
An exception from this are enemies that use special weaponry like shotguns, sniper rifles and cannons. Sniper Rifles and Cannons use the same range modifiers that player weapons use. The Advent shotgun has it’s own one, with higher penalties than the (also fairly unrealistic) long range shotgun that the player gets to use:
