My 470 rigs all pull around 900-950W dual mining. ETC @ 27-29 and Sia @ ~260

Say the system accounts for around ~50W, that's 140-150/card. Remove dual mining it drops to 750-800W per rig.

What you need to do:

Reduce core frequency/voltage (either fixed or with an offset)
Reduce memory voltage

All this can be achieved with Watttool and Claymore, no need to actually do a bios flash apart for the straps.

EDIT: didn't see you were using Ethos. You can edit the bios of your card and do the undervolt/underclock with polaris bios editor. You can typically set memory clock to less than 1000mv, try 900 for instance, even if you OC the memory.

I know that with newer 470s I got, it was "impossible" to go below 1V on the core in GPUz, even with an offset. I had to forced it through Claymore (cvddc), shut down completely and lower the memory voltage in Watttool. Then only those GPUs got below 1V in GPUz and even down to about 0.85V or less.

Note: I monitor all my rigs with wall plugs. GPUz gives an indication, but it's just the core Wattage, not the entire card, so like mushtuk says, it isn't an accurate measurement of the actual consumption of a rig.