How does the champions tab actually work?

Basically title. My current heroes on the champions tab go in order of: Top 5, Level Sync, Everyone Else. Yet, whenever I choose to upgrade Catwoman, who isn’t in Level Sync or anywhere near as powerful as my Top 5, she rockets to third on the list.

I had it as well with Green Lantern who I hadn’t touched and have got no stars for, and he was sitting at number 1. Until I put him in Level Sync, he now sits at the bottom of the Level Sync heroes as he is my weakest.

Why is this? Why do these two characters seem to get placed higher up when manually upgraded, yet shouldn’t be anywhere near the top, in turns of stars or power or anything?

Does where your heroes sit on the champions tab affect your “Top 5” when using Level Sync? Because if so, I have to purposely keep Catwoman underleveled and take an overall base power hit, just so I don’t have to waste resources upgrading the extra hero, in order to get Level Sync to work.

In an ideal world, I would like to keep my heroes all at similar levels to maximise base power, yet I have to keep Catwoman weaker on purpose, or else she again throws everything out of shape.