After the calibration the trackers have been placed in the correct places but they were all facing in the opposite direction.
I had to manually flip every tracker by setting a 180° rotation, this completely resolved the issue.
This also happens by using the official stable K2VR release.
That's what offsets are for. Only Blade & Sorcery requires this, every other game works fine no matter the tracker orientation. Other than that, they're meant to align joints with rotation overrides.
After the calibration the trackers have been placed in the correct places but they were all facing in the opposite direction. I had to manually flip every tracker by setting a 180° rotation, this completely resolved the issue. This also happens by using the official stable K2VR release.