notice the message below the "never do this" picture 2.

"Never connect the CCBEC to a combination of packs in series that results in more than 25v to the CC BEC".


this means the wiring in the picture you linked to is fine for up to 6s LiPo. Using 2 2s packs, I just connect my BEC to the ultra plug where the Y plugs into the ESC. You can put it on the ESC side, or the Y connector side, whichever is more convenient to your installation.