Then you are likely feeding too much. I like a 1:1 ratio so it's not soupy. The feed is going to nearly double in volume as it ferments.
Because it's a superfood and nutritionally dense, they need less of it. Adults need 1/2-1 cup 1-2 times a day. Mine get a total of around a cup a day and they are hefty.
Scratch is in the treat category. It's like candy, more or less. It doesn't have much nutrition. Plus, it gives a heat boost during digestion, which is great in the winter, but not good really any other time. When I feed scratch, it's dry.
But yes, there is no waste. I feed twice a day. They should eat what they need in 10-30 minutes. They clean it up, and the fines in the bottom of the bag go right in.
Seriously, I've saved well over 2/3 on my feed bill, which is HUGE for the size of my flock. I'm still kind of kicking myself for having waited so long to try it. I thought it would be too complicated; too much work. It's actually easier for me to backslop and refresh every 4/5 days and feed twice a day compared to trying to constantly monitor their feeders. Easy, easy, easy.
Molting was astonishingly easy. Their feathers are soooo shiny, which was one of the first benefits I saw. Poop smells better. That was not so much of an issue with the chickens, but oh my GOSH, what a difference with the guinea poo!
Anyhow.
. There's a full list of pros on the FAQ and lots of really good links, including to the BYC thread for FF.