My flock of 30+ goldfinches can really put away the sunflower chips, but I think I found a solution.
I was at a pet supply store recently and they were selling bags of the tiny pieces of sunflower seeds that are usually only available in the Nyjer/sunflower mixes for thistle feeders.
I bought a bag and filled two of my thistle feeders.
It slows the goldfinches way down because they have to really work to pull out the seed.
In fact for the first week I put out the feeders I couldn’t figure out who was making the little tapping sound I kept hearing on my outdoor microphone. I finally stood in the window and waited and that’s when I saw a goldfinch pecking on the opening to extract some sunflower pieces.
Eventually I will switch all my thistle feeders to pure sunflower bits in hopes of saving a little money.