Have you tried them on both, so that you know that they will eat both equally? I've tried a mix, and they're eating my brand of chick feed and ignoring the flock feed. (I bought it in hopes of using it in a dry feeder, supplementing fermented food and general foraging.)
They were eating both and anything wet.
Mostly chick starter for the past several weeks, due to young ones.
When I noticed a few weak/thin shell eggs, I added ES to the OS as they were not eating much OS. I put layer in one coop with only layers, overnight (all consumed the next morning) and the larger coop, containing the young ones, I put layer in the hanging feeder. The young ones could not reach to get the food.
Once they could reach it, I put starter. It did help with the thin shells.
There are 3 feed bowls that the layers go to immediately in the morning. I put layer in those and they are eaten promptly. When they are finished, I put the starter in them.
It doesn't take any more time, nor do I have to watch. I clean the boards in each coop, the layer pellets are finished. All containers then have only starter.
The younger ones are 15 & 18 weeks, so in a month, I'll probably do the mix as almost all will be laying. They have been laying well with good shells for 2 yrs on layer. Now, (a month) they will have 18% protein, 2% calcium.