No, we don't represent it quite that way.
An invoice, including all possible factors --such as subscription, invoice items, discount, and possibly customer account balance -- will distill down to an "amount_due", which is the amount that we will create a charge for.
Once a charge is created successfully, future actions on the charge have no further impact on the recurring billing state of the customer. For instance, refunding a a charge that was generated by a subscription invoice will not cancel or otherwise affect a customer's subscription. Refunding a charge that was generated by an invoice full of invoice items will have no effect on those invoice items. And there is no link-back or attribution that can be used to express the semantics "I am refunding X part of this invoice."
So, in short, our integration between refunds and invoices is not really rich enough to give you what you're looking for here.
If there's a refund but the subscription continues later uncancelled, it may be reasonably safe to assume that the refund was intended for the invoice items, but I realize that's a bit of a kludge. Also happy to chat off-list (jim@) if you want to go through any particular example that you're working on disentangling.
Jim