Kzem – I’m in that exact same place right now. Have worked through a few times and have landed with my bottom lip just at the lower edge of the mouthpiece/visualiser.
My sound / range / control is continuing to improve with practice but not sure whether I should be trying to find a way to keep the lower lip just inside – before I get too far down this path!
I am happy that it is mostly a very relaxed approach. Tricky stuff!