ok last bump I highly suggest trying to angle up the Sierra NrTs! Some listening tonight again, and imho it sounds really good... I guess experimentation to find the perfect toe in & upwards tilt would be necessary for the 'perfect' position, but I'm fairly confident now that I prefer the sound (seems to sound better) pointing upwards...
Maybe I'll try to do more measurements with different tilts & off-axis combinations... At listening position too, see how all compare in practicality...