Based on some things that seemed to work for me this summer,

Try making mileage saver reservations as one-way travel. Get the two secured one way trips reserved that you know you want.

Then, if the preferred date is really preferred, get that one-way award and just plan on buying the lone single one-way ticket if the other award doesn't open up.

You might also decide to check if business class mileage saver awards are available on your preferred day. They'll cost more miles, but you might enjoy that experience and then you'll know you have all your tickets for next Aug.