You can specify the grids in different banner sizes:

Millionsize-Banner (1000x90)%[GRID_5]%

Bigsize-Banner (728x90)%[GRID_6]%

Fullsize-Banner (468x60)%[GRID_7]%

Halfsize-Banner (234x60)%[GRID_8]%

Skyscraper (120x600)%[GRID_9]%