Azure Advisor aggregate score for 2+ subscriptions - how is it calculated?

I would like to understand how Azure Advisor calculates aggregations for the 5 pillars, for multiple subscriptions. 

 

In the example below we have values for Azure Advisor subscription 1 –
(Cost = 68, Security = 47, Reliability = 86, Operational Excellence = 83, Performance = 100) 

 

And subsequently values for Azure Advisor subscription 2 - 

 

 

When selecting both subscriptions, we obtain the aggregate values – 

 

Naively I might have expected that the aggregate advisor scores could be the arithmetic average between the two, but that is not the case. 

Any help is much appreciated! ❤️ 

Thank you very much in advance,

Best Regards, 

Eva