I am curious why you are so argumentative about this. I was referring to this step in the Minidsp manual that I cited. Do you find 'smooth out' an incorrect or 'very different' paraphrase of 'flatten'?
"Use the REW Auto-EQ feature to flatten the subwoofer response around the crossover region. For information on how to do this, see the app note
Auto EQ with Room EQ Wizard. Be sure to choose the correct Equalizer option (and therefore sample rate) for your processor.
There is no need to get the response exactly flat, as an additional step later will perform additional correction. The purpose here is just to get a clean crossover to the speakers."
https://www.minidsp.com/applications/subwoofer-tuning/sub-integration-rew#eq-sub
I think the OP was precisely referring to this step which is why I brought it up.