The EstimateLine Grid on the Estimates screen currently behaves as do all grids when requesting to add lines (rows). The lines must be added to the end of the list. The order of the lines, as they are added, is reflected in QuickBooks by the same order.
In QuickBooks, one can insert a line anywhere in the list; adding lines is not restricted to the end of the list. Would the Method team consider implemented this kind of functionality on their EstimateLine and SalesOrderLine grids? There are cases when the order matters and if an item is forgotten, then items must be deleted and reentered to preserve the proper order, which is tedious. (I did add a 'sort' column to the Method grid and this work well in Method but has no effect in QuickBooks.)