If a participant is taking a distribution under 72(t) to avoid the 10% early withdrawal penalty, is the participant forced to withdrawal some/all of his basis in the plan prior to pre-tax deferrals?

Example:
Acct Balance = $100,000
After Tax Contributions = $20,000
Deferrals = $70,000
Match = $10,000

In taking a monthly payment (as part of the substantially equal periodic payment), must the $20,000 be used first in distributing the account?

What does the plan document say? It could be written to have a distribution hierarchy or to be prorata from all sources.