OK, I will email the details.
For other people who might come up here later with the same question, did some more testing and found this: the combination of anything superior to DR100 + compressed RAW seem to have an influence.
– Nitro/RawPower seem to not see all the EXIF data when the RAW is compressed.
– So maybe, it doesn’t see the exposure “correction” that fuji writes in the metadata.
– Since dynamic range setting (DR200 / DR400) does underexpose the shot, if Nitro can’t see the EXIF, it can’t know that the short was underexposed then corrected.
When shooting uncompressed RAW + DR100 : exposure in Nitro seems OK. If compressed OR >DR100 the issue comes back.
Thanks Nik for the quick reply.