Yeah dosen't really help much in 3's because cleave is balanced. So i dropped imp health funnel for imp Healthstones, because once I rotate thru 2 pets my healer is already oom from spam healing my pet/me.
Anyway.
In 2's it's really nice, if you have imp health funnel (30% less damge) just start a funnel on the pet when you notice they're focusing it. Let your healer know they're trying to bomb down your pet and once he gets it back to full go back to throwing out dots/fears.
Might be helpful to set a pet stay macro built into the health funnel, I usually call it back but since your pet tries to stand next to you when you funnel it's easy for DK/rogue/Wars to focus kick/pummel/mindfreeze and quickly gib the pet.