We don´t recalculate anything - we offer the mag heading of 316 degrees, more precisely 315.6 degrees.
Here, directly from our source, what we used for MSFS:
Also, when you look for an example in LNM, using only our data, you will see the 316 degree magnetic heading. However, what we will adapt in one of the next cycles is the LOC antenna coordinates. These coordinates are slightly off, but when you use the default MSFS VHHX scenery, you will also see a slight offset for runway 31. That´s due to the LOC antenna position and not due to any heading.
We will try to adjust it slightly in one of the next cycle releases to be more centered.
Hope that helps
Richard