With an automatic, I think you'd want to limit your throttle to as much as you can give it without forcing a downshift.

Played with this some more a while ago, I think a major part of the reason that it works is that it allows you to spend more time coasting. MPG sucks when you're accelerating, whether it's a little or a lot. In the Yaris, ANY acceleration dips the MPG down into the 20's... accelerating briskly puts in in the mid-high teens, not a huge difference for the short burst of acceleration. But, if you can make the accel period shorter and the coast (using NO fuel with DFCO) longer, that's where the benefit is.