If I may...
I learned to set up in a triangle, a bit off of center.
Then I can pull a bucket sized 'line' to the tractor, X3, cutting roots as I dig.
If need be, swing out to smaller diameter to break.
Flood/soak overnight!
I like a 4 foot high minimum for leverage.
When roots around are cut, move away and use upside down bucket (last boom? at near level) on high stump to rock.
When one side/angle rocks, pull it down, leave it and fill in other side before pulling back up from that other side (creates leverage as you work).
Hope it helps!