It's at the base of the neck in the chest area. It's good to monitor their crops regularly to make sure they are filling during the day and emptying overnight.
I don't quite understand...why not free-feed at the same time so you don't have to worry about it? Pans can help catch feed so it doesn't go to waste. Chicken feeds have all the nutrients chickens need in the right amounts. Feeding too many scraps and treats can mess up that balance.
Do you free range? And do they have a lawn or pasture to forage and graze in? Fermented feed may be healthy, but by limiting their mealtimes to twice a day you may not be allowing them to eat whenever they need to.