I tried the -3db offset on my v6, result was clipping on my rears.

Front + center +3
The rears were set at +1,5, usually they are set to -1,5.

I did not experiment with other settings.

861v8, 818v3, Roon Nucleus plus, UHD722, Oppo BDP-203, DSP7200SE, DSP7200SEHC, DSP320, DSW.2, F80, 210, AC200, DSP3200, DSP3300, Ellipse