Add manual Price Component in C4C and then Request external price

Dear expert,

When we use external price logic , users can also add manual Price Component on both Product Pricing and Total Pricing for maually effecting the calculated results from ERP.

Here I have a question about add price component on Product Pricing and Total Pricing manually.When I click button "Add", a small page will pop out which I can select price component and set Amount.

However why the price component can be selected on Product Pricint and Total Pricing are different, there are less price component I can select on Total Pricing than on Product Pricing. Please refer the picture I attached to understand my question.

Where this different can be managed?

Thanks a lot.