When calculating the K value for K²S², Bentley Hevacomp Connect uses a different method than described in BS 7671.
Bentley Hevacomp Connect uses the equation from A Practical Guide to the Wiring Regulations, Geoffrey Stokes, Section 7.5.3, page 117.This allows the K value to be calculated while considering initial and limited final temperatures. Click on the image below to view full size.