Birch - cutback and new positioning

Birch. About 30 years old. I got it in 2007 when it was reportedly about 25yo, as a completely outgrown prebonsai. I left nothing from the tree I got.
After 1 year in a pond basket, I am thinking of changing the inclination again. First I vigourously pruned it. The white line I draw could be what resembles a future pot/shell shape.
Sparse foliage on the tops of both main trunk and secondary trunk, with few hanging branches, Is what I aim for.