I need a help.

My rig is Asus Z270-P/Celeron/16Gb/ Vega56 with 64 BIOS

I use this instruction:
https://www.reddit.com/r/MoneroMining/comments/74hjqn/monero_and_vega_the_definitive_guide/?sort=new

If I install 2 GPU - 130W per card
If I install 4 GPU - 160W per card

Why?