re: If an employer pays full mileage rate, does leasing make sense?

More important financial aspects of leasing are if you "must" have a new car, plan to only keep it for a short term, and can stay under mileage.

At 20k miles per year, you likely won't be able to lease.

Keep in mind leasing is just simply a "balloon" method of financing. Getting supplemental income for a vehicle really doesn't do much to affect how you should finance.