Hmm, if you want to add up the average sizes of the SiteCodes and sort by the total, you will need to know the values of the site codes. For my example, I will ensure that the values of the site codes all begin with "SiteCode:"
index=sccm Size>0 | eval SiteCode = "SiteCode:" + SiteCode | chart avg(Size) as AvgSize by Directory, SiteCode | addtotals fieldname=TotalAvg SiteCode* | sort -TotalAvg | fields - TotalAvg
I may not really understand the question, though.
And I do question the statistical validity of any chart that sums (or stacks) averages...
We are not applying a sum to the site code. The site code simply acts as an identifier for different sources of data. The point of this graph is to show the average directory size per SiteCode to notice size differences..