How to create Saved Search for Expense Reports containing Quantity / Rate?

I have some Expense Categories set as 'Rate is Required' and a default Rate applied in the Subsidiary sublist on the Expense Category.

Looking at the XML of an Expense Report, the data entered into the 'Rate' and 'Quantity' fields on the Expense sublist show up as {rate} and {quantity}.

However, when I create a Saved Search for Expense Reports (with Main Line set to False) I cannot get any data from 'Quantity'. 'Rate' doesn't appear on the drop down list, and formula fields for {rate} or {quantity} do not return results.

I can get the amount from the line using Amount Net of Tax, but I need to know the number of miles claimed (i.e. the Quantity).