You might consider adjusting the ScrollBar.Maximum property dynamically to match the size of the scroll bar's parent in proportion to pixel size or to the number of rows or lines displayed.

The maximum value can only be reached programmatically. The value of a scroll bar cannot reach its maximum value through user interaction at run time. The maximum value that can be reached through user interaction is equal to 1 plus the ScrollBar.Maximum property value minus the ScrollBar.LargeChange property value. If necessary, you can set the ScrollBar.Maximum property to the size of the object -1 to account for the term of 1.