As per their blog post.

You can now add dimensions to your
performance reports to sort and view data across multiple dimensions
including ad units, ad sizes, and countries.

This new feature allows you to add up to three dimensions to your
reports, including viewing a channel by date or an ad unit by targeting
type. To add a dimension when you create or edit a report, click ‘Add
dimension’ and select a dimension. The dimension selected is added to
the table, so you will now see two dimensions. To add another dimension
click ‘Add dimension’ and select again. You can also change and remove
a dimension by clicking the drop-down for the dimension you want to
change or remove.
Have you tried it yet? Would it make any difference to understanding your Adsense earnings?