The kmod factor is not included within the stress limits, because you could have different times under load for different loadcases or combinations. As a result you have different kmod values and different stress limits for different loadcases. This makes it difficult for AQB to use the correct stress limit for the correct loadcase (combination). The solution for this problem is, to divide the design forces by the kmod factor.
You can check this behaviour by comparing an AQB calculation of a design combination (COMB TYPE DESI) with a AQB calculation TYPE H