Scouring of the homestead threat per homestead tile

By jobifresh, in Star Wars: Imperial Assault

Hi!! My friends and I are playing the mission "Scouring of the Homestead" and we're trying to grasp the concept of homestead tiles. Are homestead tiles like zones I.e. Groups of tiles or are homestead tiles each individual tile within the red. This definitely seems to influence the amount of threat imperial can generate and is an important discrepancy.

Any input is greatly appreciated

Cheers!!