At this page, I posted an analysis of EPD hit locations when individual BBC tiles see nothing.  There was definitely a loss of counts behind "see-nothing BBC tiles," but the suppression was lower than I expected, at least via a visual analysis.  Xiaoyu Liu is doing a more quantitative analysis.

One thought was that this might be due to the fact that the bias voltage on the BBC PMTs was purposely reduced in the isobar run, so that single MIPs might not fire a BBC tile, but would fire an EPD tile.

Here, I show the results from the Au+Au run.  In this case, the BBC high voltage bias have been raised to their default values, where they should definitely be sensitive to single MIPs.

By visual inspection, I see no obvious "improvement."  Again, Xiaoyu will do a more careful analysis.