Avg() function with Aggr on Reference line producing wrong results.

[MuraliPrasath]

I've a bar chart with following Dimension and Expression.

Dimension01: ProductName& ' '& Levels

Dimension02: =if(match(Country,'China'),Country)

Expression = sum(interval(([EndDate])-([StartDate]),'D'))

Reference Line Expression: =Avg(Aggr(interval(([EndDate])-([StartDate]),'D'),[ProductName] & ' '& [Levels]))

Someone correct me on my Reference line expression? Thanks