It is the on average part you will not get - AX calculates teh PPV to the ledger on a transaction basis, if you wanted to see an average price over time and therefore a variance to standard it could be different.
I would say when anyone wants a specific report for a specific reason and the standard options do not give them what they want and you cannot convince them to use them then you write a report to achieve this. To be honest if the PPV was structured in the ledger by item you would be told of the need by the PPV entries, but this would be too extensive, but item group maybe possible as an indicator and starting point. The issue you have is with the requested report one anomaly of a transaction will cause review, so they need it at transaction level anyway, which they have!