We had a very similar feeder to combat a very similar sparrow problem (our girls were free ranging in the yard with their feeder out and I was mostly running a small bird sanctuary).
We worked with the girls for weeks on the feeder, just absolutely no dice. I hope your girls get it.
We gave up and switched to the
Revolutionary Chicken feeder (there are other sizes on the site, too). It's been - as the seller says - rain-proof and mouse-proof thus far. And the girls got the hang of it the same day. I don't know what your budget is, but I felt a big sense of relief not having to go back out to the run to once again show my irritated, hungry chickens how the feeder worked.
It also keeps my food-guarder from being able to see that her sister is eating, since the tubes act like blinders. Honestly, it's the best thing I've bought for the birds. Good luck!