This is what I use. I cut the socket end off, and slip it over the narrow end. Makes the elbow a little shorter. but I think some people use it as is. The longer the reach, the less waste, but could be hard for small birds.
Chicks don't eat that much. Is it that big of a deal if they waste food? I have different size PVC street elbows on a 5 gallon bucket, from 2" to 3.5". I think the chicks start using 2" elbows at about 4 weeks old and then move up.