The cable included in the pack you link to is an attenuated cable - that means it is designed to reduce the Zoom's output from headphone/line level to the mic level input that your camera is expecting. Because
Because the cable is doing the reduction, you will probably need to leave the gain on the camera at it'sits normal setting for a directly plugged in microphone and/or adjust the gain on the Zoom so it is peaking higher than -12dB−12dB. One good thing to try is setting your camera up with Magic Lantern (http://www.magiclantern.fm/Magic Lantern). You already have adjustable gain on the camera, but ML will add amongst many other things on camera audio meters so you can see the levels that your camera is recording, not just the levels the Zoom is picking up. I
I assume you have seen advice on the likes of YouTube to set the H4Ns gain for about -12dB−12dB, and reduce the camera to virtually no gain. Good advice, but for people who haven't paid for a specific ATT cable. The ATT cable should give better results than trying to fudge the same effect by adjusting gains everywhere.