When you are seeking to improve the shape of your trees sometimes you need to reflect on that broad triangular canopy that you associate with both mature parkland trees and established mature bonsai.
As your trees continue to grow and develop every so often you will need to intervene and retrieve the shape of its canopy. Sometimes you may be able to get a result with some selective pruning but eventually it will more than likely need another complete wiring.
Continually redefining the triangular canopy is part of your ongoing bonsai maintenance work but each time you do this you are lifting your tree to his next level.