Tactics at the level of 6 characters exist in almost all RPG games. Starting with "Fallout", "Baldurs Gate", "Arcanum" and ending with modern games. The role-playing system of these games and the game world itself are worked out better than Xenonauts.
And if I have to make a choice: to develop 6 characters in Xenonauts or to develop 6 characters in RPG games, then the choice will not be in favor of Xenonauts. Xenonauts do not have a good role-playing system of abilities, skills and character characteristics for tactics of 6-8 people.
But there are much fewer tactics for 8-12 (or more) characters. This gaming niche is not so densely filled.
(The fact that the original (canon) UFO: 1-2 X-COM: 3 Apocalypsys were platoon tactics, and, apart from them, there are no more turn-based platoon tactics (12-26) - I have already said many times. This is the only unoccupied gaming niche that gives the player such gaming sensations (experience) that other games are no longer able to give.)
In general: For part of the tactical battles, the game should increase the number of aliens by 1.5-2 times. The complexity of the battles should be different. There should be missions where the player is "resting", and there should be missions where it is "difficult" for him.