Talking to one guy on the trail, he would tighten his levers just to the point that if they hit something, the levers would twist on the bar, saving the levers from breaking. I would imagine if they were low enough to hit the frame as the bars spun around it would help there as will in a crash.
I believe, for both my Chiners, the bars clear the frame. I like to sit a little more upright (XC style) with a few spacers below the stem and riser bars so there is no direct contact between my bars and frame if spun around.
So my best recommendation is to set your bar height such that the bar end clears the frame.