Sounds like you feed your flock properly. Some people may try to avoid giving them too many veggie scraps or eggshells, but we feed ours as long of the eggs seem fine. The only potential problem could be onion-tasting eggs from onion scraps, or rock-hard eggshells from too much calcium. All easily fixed. We also mix cracked corn with our Layena (Purina Brand layer pellets) in a 2 part corn to one part layer ratio. They seem to be just fine and our flock of 16 hens lay close to a dozen a day! Basically, don’t worry too much about quantity or type of feed, as chickens diets are very flexible, and their eggs are a direct indicator of any problems!
If that works for you.
Layena is a high quality product but Purina intends for it to be fed as the sole ration. Mixing it with that much corn isn't a good idea. Printed on the feed label is this statement.
Feed Purina® Layena® free-choice as the sole ration to free-range and confined laying chickens (including backyard egg producers, small to medium breeds and fancy and exotic breeds) after 18 weeks of age and throughout the laying cycle.
https://www.purinamills.com/chicken-feed/products/detail/purina-layena
I'm surprised you're still getting eggs. The main ingredient in Layena is already corn. Mixing 2 parts corn and 1 part Layena (16% crude protein) will yield 10.5% crude protein. That's much too low for body maintenance, metabolism, especially of the immune system.
Moreover, corn is low in some essential amino acids. Your mix is providing your birds with 0.4% lysine while a minimum of 0.75% is needed.
There may also be some vitamin and mineral deficiencies from that practice.
I hope your birds free range on some pristine forage so they can compensate.
https://www.nap.edu/read/2114/chapter/9
http://www.merckvetmanual.com/poult...mino-acid,-and-energy-deficiencies-in-poultry
https://www.ncbi.nlm.nih.gov/pubmed/6847546
Excessive calcium is a problem but not as you describe - causing rock hard eggshells.
It isn't a direct correlation of input and output. In fact, excessive calcium, if it creates an imbalance of the calcium/phosphorus ratio, can cause weaker shells.
Egg shells are calcium carbonate. But after the intake of calcium carbonate, whether that be from oyster shells or egg shells, it is broken down by digestion into calcium 40% of the total and carbonate. That then has to be reformulated into calcium carbonate in the shell gland but must also have proper levels of phosphorus, vitamin D3 and to a lesser extent, magnesium.
Excess calcium must be processed by the kidneys leading to atrophied or enlarged kidney segments.
http://edis.ifas.ufl.edu/vm013