Guys, I'm getting all the information I can before making parts purchases for my first AR build and I have a question. I was going to get a 16" barrel and the MKM AR-15 KeyMod for a Mega lower. I want the barrel to stick out past the rail by about 2 - 3 inches. Which version of the KeyMod rail setup should I get? I know the sizes of the rails are as follows:

Extended Rifle = 14"
Rifle - 12"
Mid-Length = 9"
Carbine = 7"

Is it as simple and getting the extended rifle version for 2" of stick out? I guess not knowing where the dimensions are taken from is the real question here...

Thanks

extended