The balancer is responsible for selecting players. The balancer "checks" your highest tier ship and amount of battles on this ship. It's set as priority for balancing. So if 2-tier and 5-tier ship meet in the battle it means that:
a) 2-tier ship has many battles and isn't considered as newbie
b) 5-tier ship has few battles and isn't upgraded
c) for some reason players take lower ship having higher ships in the port
Moreover, some ship levels are united into one ship group.