I mix all the formulated feeds I need (starter, grower, layer, etc.) using a recipe Fertrell the fertilizer company publishes. It is essentially corn, soy, oats, aragonite (calcium) and a nutrient blend by Fertrell. Also fish meal in the Starter. I can now modify it (add wheat, extra corn, etc.) depending on if I want to change it for any particular reason.
This I feed regularly in the evening, with scratch in the morning, grass all day and as many scraps as I can get. Sometimes I will replace feeding scratch or mash with scraps if I have enough.
I look at the mash more as a small fraction of their diet, supplementing everything else as opposed to everything else (grass, scratch, scraps) supplementing their main diet of mash. Many people wouldn't agree with that though, saying they need just mash since it is "scientifically formulated".
Here is a link to the Modern Homestead, Harvey Ussery does a lot of neat feeding things with his flock. I have met him and he is a very interesting guy -
http://www.themodernhomestead.us/
Best of luck on your chicken feeding journey, MW