I found out that when i mine other coins, especially the coins with low energy consumption(like X11 coins), at the same time mining XPM without turning the rig off, it gives me almost at same speed of XPM and little shrinkage of other coins, can Claymore or someone else explain this
eg, i use 290,the 4ch is about 150000, first i turn on the xpm miner, after a while, i turn on the other miner(cgminer), the 4ch almost kept the same, and cgminer about 70% percent of full run