I have an Imperial Squad (Justice_League) and we have only a single loss (which we avenged) and over 40 wins, but that's about to change. Our breakdown is this:
1 - 9: Newish with only a few upgraded weapons and troops.
2 - 8s: Newish with only a few upgraded weapons and troops.
2 - 7s: 100% maxed except Droideka.
4 - 6s: 100% maxed except Droideka.
5 - 5s: 100% maxed.
1 - 4: 100% maxed.
I believe that the more your squad wins the harder your match-up becomes. The squad rank and trophies have nothing to do with it. Our current war is completely unwinnable, they are going to 100% us and we hold all the outposts. They have: 1 maxed 10, 5 maxed 9s and an 8. The only reason we beat them the first time was that they didn't try very hard.
Their total HQ level is 104 compared to our 92, and again, they are maxed out at the top. War search both times in getting this squad was really quick, minutes and we've got them back to back. There has to be some alternate number that they are using to determine the wars, and I think it's got something to do with your win percentage.