in the config file comment there is no documentation on what lay_coefficent does, and it appears to be 1.0 for all chickens

Maybe it is with how I read the example text at the top of the config file, but I understood the "lay_coefficient" as a quantity multiplier for the item the chickens are supposed to drop. So instead of changing how fast the chicken produces an item (which is already altered by the chicken's growth, gain and strength stats), it changes how many items are produced per chicken when they finally drop.

In Curseforge.com, the description of this mod claims it is "heavily customizable: change laying rates, items, disable chickens, modify breeding, set drops, ...", so I assumed lay_coefficient would affect the rate at which chickens lay items, acting as a multiplier to their growth stat. However, after some testing, they lay items just as fast with "lay_coefficient": 1.0 and "lay_coefficient": 0.001. It would definitely be a good idea to tell players what this does.

Having a brief look at the code, it looks like lay_coefficient affects the frequency that chickens lay eggs, as a multiplier of "time between lays". So setting it to 5.0 would make chickens wait longer between each lay, and setting it to 0.5 would make chickens lay more frequently. If you're more curious than me in how much the coefficient affects the frequency exactly, and are not satisfied with my lazy "more or less frequently" description, you can look in the EntityChickensChicken.resetTimeUntilNextEgg() method.

The coefficient seems to only affect free-range chickens and has no impact on roost chickens. I can only see it referenced when a chicken outside of a roost lays an egg; it is not referenced at all in the roost.