I don't know if this help some other user but I think i have find a solution to slash the reject.
I use one rig of 4X R9 270 (not 270x !!!)
I just change two paramter from my config.
I move to sgminer 4.1.0-73-g80e6 from cgminer 3.7.2
I use the "alexkarnew" kernel
And now I slash my reject by 4, i have now 1-3% reject.
My theorical hashrate is a bit slower ~ -2% minus but my WU (~+5%) and my detect hashrate on the website are better.
Whats your kernel path?
My sgminer seems to be using ckovilas kernel with the kernel path set to /usr/local/bin.
I've moved the files out of the kernel folder and into the main sgminer folder and changed kernel path to "."
Update: https://github.com/veox/sgminer/issues/49
Removed the kernel path from the conf file and using -k zuikkis. Moved the kernel files from kernel/ to the sgminer folder. Now using zuikkis kernel.
Kernal path is /usr/local/bin
After compiling sgminer make install copy all kernel and soft to /usr/local/bin/
To R9 270, my config is:
GPU engine: 1000 Mhz
GPU Memory: 1500
Intensity: 17
vectors: 1
worksize: 256
thread-concurrency: 12992
shaders: 1280
gpu-threads: 1