Well, first, the 1/2" average is an average. It could be more or less.
Last I checked my hair, at 6 weeks I had .75" of NG and now at 11 weeks I have about 1.5-2" depending on the spot. I should be see 2 inches in 16 weeks, but I am seeing it in 11.
I exercise 4 days a week religiously, mostly strength training (because cardio should not be a focus for women) and I notice when I do less cardio, I have better growth.
I do not really eat meat (mostly on occasion) mostly eating seafood, veggies, dairy by-products, soy, and fruits. I keep fried foods to a low and processed foods to a no-no
Fast food is not in my food vocabulary. I put myself on a coffee (maybe tea or hot chocolate depending on the time) and water restriction. Basically, during the work day, I can only drink coffee (after 3 I will drink tea or cocoa) or water. When Im home, I drink water, tea and 100% juice, but mostly water. I do not drink soda. Since denying myself juice, I have noticed stronger, shinier growth.
Last, I take prenatal vitamins only.
I sound crazy and disciplined right? I have noticed that by 4 weeks post, I always have NG. This has been my habit for years. Whether it contributes to better growth or not, I cannot say, but better health and lifestyle will lead to better healthier hair. I just think a better diet and lifestyle will lead to optimal health in the body and hair will reap the benefits.
Remember, hair is the garbage dump of the body. So if you treat yourself well, there will be more to give hair, instead of it getting the bare minimum due to poor eating. So if you eat well, you will have the best growth. But a poor diet will contribute to slower growth that we may mistake for regular.