Confusing math from Encore Viewer

I've used the search function and found a number of references to poor math used by Encore Pro and Viewer, but this is causing some head banging on my end and I don't see how they are computing the reported output.

For example, last night I had a reported apnea index of 1.8 for 7.2 hours of sleep. This would imply that during that 7.2 hours I had 12.96 ( 7.2 x 1.8 ) events of apnea. However, when I look at the raw data (done by importing the XML file that Encore Viewer generates into an Excel spreadsheet) there are only 3 apneas recorded. Also, the Daily Details graph accurately plots those three events. So, how does Encore Viewer report an OA index of 1.8?

It gets even more confusing when I look at the Daily Events per Hour table at the bottom of the Daily Details page. If one takes the MaP/60 (minutes at pressure divided by 60 to give hours at pressure) multiplied by the OA events per hour and then sum that row one should get the total number of OA events. If I do this calculation I get a total of 13.04 OA events which is within roundoff error of the 12.96 needed to make an OA index of 1.8 for 7.2 hours of sleep. While this number is at least consistent with the reported OA index, I still don't see how these numbers are being generated.