If the distribution from the Roth 401(k) would have been considered to be an entirely nontaxable qualified distribution (Roth 401(k) 5-year period met and over age 59½) if paid to you instead of being rolled over to the Roth IRA, the entire amount rolled over to the Roth IRA became contribution basis in the Roth IRA. Otherwise, your basis in the Roth 401(k) became corresponding basis in the Roth IRA.
Distributions from a Roth IRA are not pro rata. They follow Roth IRA ordering rules.
