You can effectively lock yourself out of choices in Triangle Strategy, unfortunately (meaning you cannot sway the decision a certain way no matter how much info you collect and what combination of answers you try). Each decision corresponds to one of the three convictions, and if you don't have the necessary amount of points in that conviction at that point in the game, you cannot say or do anything to sway certain characters (you can grind it in very miniscule ways but that takes ages).
I loved the game overall and enjoyed it a great deal, but this was also my sole complaint. Especially since they're a lot more transparent about it in new game+, and (spoiler about routes) there's a golden route that sounds pretty much like the true ending (I'm still working on it, so I haven't seen it yet myself), and you need to make very specific choices at these junctures to unlock it.
Also, I'm not 100% on this, but I read that battles scale based on your army's level and maybe the difficulty. I was also wondering why I always like 1-2 levels behind the recommended level, but apparently it's designed that way. They give you a lot more exp when you're somewhat underleveled vs. being at or above the same level as enemies to make up for it. I felt like I had to grind more for money than exp just to get enough upgrade materials.