Looking at avarage is pants.
For example, you've had 9 weeks of taper and 9 weeks of recovery, so in those 18 weeks your mileage would, sensibly, be less than your peak mileage weeks. To do otherwise would only cause you to race poorly, fail to recovery, incur injury or illness.
Doing such endurance events means that your training is going to look like a seesaw.
If you were running shorter events, say 5 or 10k or not racing at all, then your mileage would be more consistant. It's easier to hold high mileage when not racing or when the only races are 5 miles long.