I tightened the screws 10" to 6" zero length reducer flange to 34 Nm in which most of the flange contacted the vacuum cube and the copper gasket could no longer be seen. It took 40 Nm to tighten the screws on the 10" diameter electronics flange such that there was this contact. This is a flange from the Holometer, so maybe they require this higher torque spec. Alternatively, this could be a coincidence. There is a small notch milled out of this flange, but it shouldn't make a difference.