Throughput Time calculation and customized calendar

Good evening everybody,
I have set up a customized calendar in the IBC datamodel and I was expecting that all throughput time calculations in all anaysis based on that datamodel would reflect these settings, but I was surprised to noticed that only Process Explorer, Variant Explorer and Throughput Time selector are affected by this customization.

Basically, when using the CALC_THROUGHPUT this calendar setting is ignored and TPT gets calculated on a 24x7 basis.

I guess I could do something by mixing PU_FIRST, PU_LAST, WORKDAYS_BETWEEN functions, but this strange standard behavior makes the CALC_THROUGHPUT function basically useless, as a workdays/workhours calendar is always needed in order to correctly calculate throughput times in reality.

Am I doing something wrong?
How can I calculate throughput times (using CALC_THROUGHPUT function, which per se is very easy to use) taking into consideration the customized calendar o a factory calendar?

Thanks for your help, kind regards,
Andrea