This is probably what I would do: start at 9 miles total volume, but move it outside. Your race is going to be outside anyway, so you might as well train outside.

Day 1: 2 miles
Day 2: 2 miles
Day 3: 3 miles
Day 4: off
Day 5: 1 mile
Day 6: 1 mile
Day 7: off

The second week add 10% to each day: 2.2, 3.3 and 1.1.
The third week add 10% to each day: 2.4, 3.6 and 1.2
The fourth week back off and only do 70% of the 3rd week: 1.7, 2.5 and .9

Then repeat the cycle, only use the previous cycle's week 3 mileage for the starting week mileage of week 1. Keep doing this until you reach your goal. Resist the urge to add more than 10% on the build weeks, even if you feel good. Only adding 10% or less is how you keep feeling good.

I know the percentages aren't exactly 33% above and below the medium run, but at the lower volumes this isn't as critical. As the base mileage is built adjustments can be made to get the numbers evened out a little better.

Anyway, that's my suggestion. Take it for what it's worth. I'm not an expert or a personal trainer or anything like that. Just a guy who's been running for a lot of years and figured out what works for him.