I'm a bit confused on the cost. For a 2 min call the pricing estimator gives me $0.25. Similarly, the assistant page gives me $0.12/min. But then actual cost of the call is $0.52. Could it be that I'm using a knowledge base and this is somehow not reflected on the assistant page? But then if I copy the total number of prompt tokens according to the call cost page, and input them on the pricing estimator, I still get the same number. So I'm confused?