Same plane just means that they're all on a two-dimensional doubly ruled surface spanned by two linearly independent vectors. Like if they all abut the same wall.

Set the phase to 0 degrees.

Set the cross-over to 60Hz. Any higher and the bass may become over-powering in that room.

Remember there's an app for that sub so you don't have to get your ass out of bed. There's a lot of fiddling you can do with that app. Have fun!

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated