Adjusting the Height of Stacked Y Axes
1.If the diagram is in a document or a worksheet, double-click on the diagram to open it.
Using the mouse:
2.Drag the dividing line between the two diagram planes to the desired position.
Using the Properties window:
2.Select the Y axis whose height you want to adjust.
3.In the Size percentage field of the Properties window, specify the desired height of the axis relative to the overall height of the diagram.