Best practice would be to place the subwoofer vaguely in the plain of the L/R speakers. Placing a subwoofer next to your listening position would result in a somewhat disjointed sound stage because the L/R would originate across the room from the subwoofer.
There are two benefits for a subwoofer. Obviously, there is more bass, but there is also increased midrange clarity because the complexity of the music rendered by the smaller speaker is reduced.
You will discover that subwoofer placement affects the outcome. Moving the subwoofer or your listening position a foot or so can have a very obvious impact on the results.
Thank you! What settings do you keep yours at? @buzz
My settings would be extraneous information for you because our rooms are different and I’m using a SONOS SUB, not the Mini.
Only you will know what sounds “best” (to you). If you are experiencing issues, describe what sounds wrong to you and we may be able to offer some suggestions.