Actually things are not the same.
First EN-13480 defaults (in CAESAR II) to using Appendix H.1, so the SIF is the same for both in-plane and out-of-plane. When using H.1, there are no weldolets, sweepolets or extruded welding tees recognized. If you select one of these fittings, CAESAR II changes them to an unreinforced tee. So the flexibility characteristic is "2 * en / dm". This is why you get different results.
If you want EN-13480 to use Appendx H.3, then you need to go to the Configuration Module, on the "SIF & Stress" tab, and check the checkbox to allow this code to use different in-plane and out-of-plane SIFs.
Additionally, for B31.3 weldolets, the in-plane and out-of-plane SIF equations are the same - hence B31.3 will yield the same SIFs while EN-13480 will yield different SIFs.
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Regards,
Richard Ay - Consultant