From the picture, we are looking for the part that is the front of the table. These 2 examples must use the wass line on the 2point side because the side marked with the red line is the longest. This is the side that will make the diameter of the diamond the widest as well.
From the picture, it can be seen that these two examples require drawing a dashed line on the 2-point side, as the red line is the longest. This is the side that makes the diameter of the diamond as wide as possible.
As can be seen from the figure, these two examples need to use the wass line on the side of 2 o'clock, because the side of the red dotted line is the longest side, which will make the diameter of the diamond the widest.