I was also dissapointed when the schedule recently opened up and I was unable to book award flights the day the schedule opened. Not sure how that is capacity controlled, but luckily I kept checking and the exact flight I wanted opened up and I was able to book it.

I have also had trouble on every Sunday this summer. I have been pretty lucky on Friday flights on awards, but I have had to pay for every Sunday this summer. I guess it is to be expected.