Zigbee Xbee pro s2 security threads

i want to know, what is usage of EO (encryption option) at xbee-pro s2 “END DEVICE” side. For Coordinator side there is EO=0 for transmitting key OTA and EO=1 for Not transmitting any key while joining new device.
but i didnt understand, why they gave the same option for end device. i checked all possible combination and sniff the data but every time same response, i got.

so please can anyone explain me, what is usage of EO option for END DEVICE??

The EO functions on the Router and End device tell the nodes exactly how to work with the encryption keys and functions.

please can you elaborate more.
i already tried the possible combinations but dint get any deference.

EO 0 on both works. This allows them to associate without transmitting the Keys as you have to manually enter it.

EO 2 on the Coordinator and 0 on End devices and Routers also works.
This works by using the network key to encrypt the keys.