Ranked Summon is not necessarily the main team's summon. Ranked summon is the summon that you currently that the set line up. So if you're on set 1, your ranked summon is based on set 1. If you're on set 2, ranked summon is based on set 2, etc.
So what I do is that I have set 1, 2, and 3 have maybe the 3rd summon all the same. Then in Ranked, I choose the 3rd summon. So regardless of which set I choose, I know my ranked summon is unaffected.