Not sure if this is possible but most of my sales are size variations would be good to see what is actually selling best at a variation group level

We found a workaround for this using an extended property called Parent

When we report on sales we use a custom query which also includes that extended property and when put into excel reporting tool it auto sums for us. 

We found this works better than on a variation group level because due to the way different channels work such as Amazon - Ebay - Spartoo etc we have different Variation groups setup on a channel specific level. 

So Amazon allows size / colour only where Ebay we could have more variaition themes and need a new VG to handle those. 

By reporting sales on the actual Item parent using the extended property you can get a proper picture of how many of each item you are selling instead of a potential amalgamation of items in the same variation group. 

Or that is true in our case. 

Thanks - that's a good idea!