I currently have JTables nested in JScrollPanes like so:

My problem is
If you use MigLayout, when add the scrollpane containing the JTable, you can specify the constraint growx instead of grow, to make it stretch only horizontally.
Now the scrollpane is located in the middle of its parent. You can set in the row constraint to make it align to top of the row. Or, in component constraint: aligny top.