Only used when the rowHeight is greater than 1, in the case where the last row is partially displayed due to an uneven number of physical screen rows compared to the row height. For example, 10 screen rows provided to display rows that have a row height of 3.
If the row height causes rows to be chopped-up between screens, set this to the last screen row that row data can appear on. Leave zero for normal processing.
When this value is not zero, and row height is not an even multiple on the screen, extra values and logic is activated in the field map's processing class to handle the wrapping between screens.