Think about how it works - logically, after each xover point change, it's going to change its DSP settings.
I would never play a 4 or 5 down to 60, and the 4 I wouldn't play below 100, and I have been doing this for over 20 years, so I'm not clear on your problem there.
I select 20 hz and 6dB if I want no subsonic.
Remember that the sub level control also boosts the midbass ABOVE the xover point.
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