Glad you’re doing well and enjoying game :)
As for fights with gheists, 4-5 tiles may or may not be enough. It’s already quit far for effect of banner and rally ability. You want maximum 3 tiles in ideal case. Of course that’s not always possible. That’s why second sergeant can help here. I tend to always have one spare sergeant in “learning” in case my main one dies. That comes handy for those fights against gheists.
Difficulty of the missions is somehow random. I had both more and less difficult missions for their rating in stars. Either developers did that on purpose or it’s simply case of computer code being unable to properly combine all the attributes to calculate proper difficulty for you. there are just too many things to take in to consideration.
In either way, it keeps player being vigilant so I like that it’s random to some degree. Makes things bit more unpredictable and fun.
Direvolves certainly are not allied to raiders. It’s just that enemy AI seems to be programed to go after weakest target it see. Which in that case was probably you, that’s why both groups went after you and did not engage each other. However if battle would start, they would be hostile to each other on the battle map. Problem is, Direvolves are really not something you want in a multifight due to reasons I have mentioned before.