If in a team with acceptable team performance a role can be filled with more than one person, there are two options possible: Either this position is critically important for group performance. Then each of the persons on this role in successful teams can be considered as being an ideal choice. Or this position is less than critically important for team performance. In this case the position can be staffed non-ideally and nevertheless group performance remains acceptable.
The more ideal staffings exist and the less important the positions are for group performance, the more combinations of different persons can be observed as being successful. A non-ideal person on a position endangers the success of the whole group. Group performance possibly turns inacceptable - the more important the position of this person is the more likely group failure becomes. The influence of several non-ideal filled positions adds up to a value that determines whether group performance as a whole is above the threshold of acceptability.
The ideal person in a position and the importance of a position for group performance can not be read directly. They solely can be inferred from comparisons of different successful combinations of team members. Only one statement is sure: In all teams with acceptable performance the positions staffed with non-ideal team members these non-ideal positions are not important enough to let these teams fail.