Hi There!
It sounds like your orpingtons just started alaying a little while ago, honestly the only thing that will make your chickens lay huge brown eggs is following the common principals of keeping chickens. Such as making your chickens stress free, always have a good amount of food and water available to your hens and keeping the coop clean. What might help for getting large brown eggs are putting grit in their feed and using the "Sav-A-Chick" medication in your hens water. Sav-A-Chick is meant to provide baby chicks extra vitamins and help their digestion. However, on the back of the product it states that adult hens can use this product and it will benefit them. If you aren't fond of this product there are many other vitamin powders for chickens that you can use in their water. Other than that just keep doing what your doing!
Hoped this helped!
Sunshine Ducky