Pizza Hut Delivery Driver mileage reimbursement......?

I am a delivery driver for Pizza Hut. The store I work for is not franchise owned, it is owned by Pizza Hut, i.e. corporate. Recently, corporate changed our pay rate to a "tip credit" in which we are paid $3.00 less than minimum wage while we are dispatched on a delivery. While I understand this is completely legal as I have done my own research, I am little concerned about our mileage reimbursement as we use our own vehicles and always have. (Mileage reimbursement remains the same as it was before the tip-credit pay change). Pizza Hut charges a delivery fee of $2.00 to the customer for each delivery. Pizza Hut tracks our mileage at a set 4 miles per delivery. However, drivers are never asked to report their actual mileage at the end of shift, it is a set 4 miles per delivery. Of the $2.00 that is charged to the customer per delivery, we receive $1.35 of that as reimbursement. If I do my math correctly, $1.35 divided by 4 miles equals 33.75 cents per mile. As we use our own vehicles for deliveries, the Federal standard for mileage reimbursement is 51 cents per mile. Obviously, 51 cents multiplied by 4 miles is more than the entire $2.00 delivery charge, meaning something doesn't add up. Is it legal for Pizza Hut to only reimburse us 33.75 cents per mile when drivers are not asked to report their actual mileage and are using our own vehicles? Is it also legal that a set-in-stone $1.35 be reimbursed to drivers per delivery or should this be done based on the Federal rate of 51 cents per miles based on actual mileage? And because we are never asked to report our actual mileage, we do not keep record of this as Pizza Hut has record of it, recorded at 4 miles per delivery. My understanding would be that if Pizza Hut records our mileage at a set 4 miles per delivery, we should be reimbursed $2.04 per delivery. I keep a spreadsheet which shows my tips, reimbursement, total amount of hours, total number of deliveries, etc. since I started with the company in February of this year. Do I have a case to seek reimbursement for the 69 cent difference in reimbursement ($2.04 minus $1.35) multiplied by the total number of deliveries I have had since I began with the company?