It is supposedly controlled by the Preferences page, Network usage, Additional work buffer. The number to keep in reserve is calculated by your return rate. Normally, it works pretty well.

However, I believe that problems related to their recent crash are echoing down the halls, so to speak. My main box does two every 3 1/2 hours and I've got it set for a 1-day buffer. This normally gets me about 8 WU's in reserve, besides the two being worked on. Right now, all I get is two.

You could give it a bit to get cleared up or risk the wrath of the admins and post a trouble report.

Bok & I have been hammering them about the 3rd-party stats, which I see MAY now be working. Or trying to.