Just a few questions:
Are you using a modified bmminer? And are all your miners on 4 flexible tubing? If yes to both then you should be underclocking your miners while using 4 tubing. If you have to use flexible tubing you should be using 6 tubing because 4 is too restrictive especially with longer runs.
Yes modified bmminer but did not overclock.(the same problem in the original bmminer ) . "" 6 "" Can't understand, can you explain? My English is bad, I'm sorry. I'm waiting for your help