How can I use header level attribute of Request for calculating list price from CPQ Pricing Portal.

Summary:

In Pricing Portal I did not find any provision to include PriceBook. So I created a Header level Pricing Attribute called "Price Book Name (priceBookName_c)" in Pricing Portal and used it to create a condition for the Pricing Model. However while calculating the list price using the calculatePrice Rest API (/rest/v16/pricing/actions/calculatePrice), its not taking the "priceBookVarName" from the request header but I have to pass value to the attribute priceBookName_c in the "headerAttributeValues" section of the request. How can I use the header level value of priceBookVarName for calculating price from Pricing Portal.