It isn’t the “vacation rate” exactly.
You have your base pay that the vacation and retirement contributions are based off of then you have what you actually earn including overtime (most AMO contacts the overtime is automatically calculated and you make a flat day rate called the “working base”).
You might have $350 benefits base and $500 working base and with a 30/30 vacation plan that’s $850 per day worked.
Your AMO Defined Contribution Plan and Money Purchase Benefit Plan contributions are based on the $350 per day rate.