Yes, mine goes down, but that's also why on the first page he says to experiment with the correct dcsi for it... Don't forget you can hit 'S' while it's running to get the stats, and '+' and '-' to adjust dcsi.  This way you can tune the maximum gain for the secondary mining, with the least impact on Ethereum.  For instance, my dcsi is 50, I loose about 1-2MH (like 1-2% of the rig total) of eth, but it's almost 2.5x on the secondary side.