DB plan has employee contributions. Participants wants to receive monthly employer benefit and withdraw employee contributions+interest and then rollover only the interest portion. In that case, no part of the cashout will be taxed now, however, am I correct that since taxes are spread out between cashout and monthly payments, the basis is different from the rollover amount in this case? Here is a simplified version of the calculation:

Post tax employee contributions 10,000 Already taxed
Interest 20,000 Not yet taxed
Total 30,000

Monthly Benefit
EE Part 500
ER Part 1,500
Total 2,000

# payments 210

Excludable from tax 2,500
Taxable 27,500
Total 30,000

Excludable from tax (10,000 - 2,500) / 210 = 36 (of monthly benefit)

So, although $20,000 is rolled over, only $2,500 of that is actually taxable upon withdrawal?