To be calculating you must be capable of rational thought . The philosophical framework that exists for the Iranians is not that of “Western civilization” . If you take this simple fact into account & can get some idea of exactly the Iranians think you can understand that in their way they are in fact rational.
Well, maybe they are “rational” by some measure, but they accept false assumptions as givens, so they don’t arrive at rational results. Garbage In, Garbage Out.