Some of mine are smaller then others even though they are raised the same. I have only raised chicks with a broody hen so don't know any different comparisons.
I either feed starter or grower with shell on the side since there's often chicks in the flock and always roosters in the mix. 20% protein in starter and 16% in grower. Problem is they have anti-cocci meds in it - but natural type ( Orego-Stim and ENTX, plant extracts ) so ok for layers, theres no other option for feed without meds unless it's layer feed and I don't want that for chicks or roosters

so they have the 'natural' anti-cocci med all the time hopefully no harm done