The trick is to have your ranked summon be the same and on same slot in all 3 sets, that way no matter what set you change to, your ranked team will always use the same summon because it keeps the same slot. Yeh it's weird but it works fine once you set it up.

If you want to use Snake for ranked just have each of your sets with Snake on same slot.

Set 1: any any Snake
Set 2: any any Snake
Set 3: any any Snake