You can cover the same size of area with landfill by using less landfill.
The trick is to draw a 1xN line with landfill and leave one space and draw again a 1XN line. With this method you use up less landfill than using a NxN landfill.
For example:
Cheap landfill
Thanks for your answer in advance.
I used 7 landfill with the cheap method, and used 20 landfill using a 3x3 landfill