EUA runs EVERY night, 7 days a week. Remember, just because there are F seats when you check in the daytime, that does not mean there were F seats when EUA ran the night before. There are threads on this which list all the various reasons why this is the case.

That being said, I do find that sometimes, rarely I would have to say, but sometimes, I can see an F seat available right through my EUA window, and not correctly assigned. I have to say that with respect to CO flights (NW different story) EUA seems to work pretty darn well.