Another way to think of it is to count the blocks.
In a 9 across 10 down setting straight set you need 90 blocks. Assuming no sashing and no border you will have a quilt that is 81 x 90 (7,290 s/i)
If you take those same 90 blocks and turn them on point you will only get 6 across and 8 down. The resulting on point quilt made with 90 9" x 9" blocks set 6 across and 8 down plus adding setting triangles will measure about 81 x 100 (8,100 s/i).
The additional surface area is due to having to add the setting triangles.
The OP will need to make more embroidered blocks or add plain blocks to get up to the size Dunster illustrated above.