FWIW, you're not going to get much trunk thickening in a container with the JM. Restricting root growth in a container is one of the last steps in developing a bonsai. If you want to thicken the trunk, give the tree as much room to push roots as possible and allow it to grow. The ground is the best place to do that. Larger containers can do it, but more slowly and you have to balance not using a container that is TOO large--Larger containers can be a problem since they have more soil that can stay wet and actually inhibit root growth.
The first stages of growing a trunk are a balance of getting to the diameter lower down that you want THEN chopping at a location that will produce taper with new leaders. The trunk and nebari are developed FIRST by growing the tree as much as possible. That means no pruning, allowing as much growth on the top as possible. Growth up top fuels the increase in diameter lower down. Once the tree has reached the diameter you want (this is a matter of preference and plans for the size of the "completed" tree) the tree is chopped. So you have to decide what you want to do with the tree, do you want a smaller shohin-sized maple, or a larger bonsai? Decide that work towards that goal using the grow out/chop back.