“max” value in singlestat panels

I am using v3.1 and works with elasticsearch 1.7.3。 I added a “singlestat” panel and try to calculate the max value of “total_users”. In metrics tab, I selected “max” to replace the default “Count”. however, after all is done, I find the actual value shows up is not the actual "max"value, but seems work correctly after I set the interval to "1y(year). Then I find another "max” option in “option” tab.
Any advise the difference about “max” option in the 2 tabs?



The max in query is for elasticsearch query backend to process, instructs elasticsearch to pick max value of the group by date histogram interval, the max in options tab is tells singlestat panel what value to show in case the query returns many data points