It might be a little hard to understand from the explanation, but basically you are trying to “fill” the field so that the aliens do not have space to move anymore.
Ito ay maaaring maging isang maliit na mahirap upang maunawaan mula sa paliwanag, ngunit isa lamang na sinusubukan mong “punuin” patlang upang ang mga dayuhan ay hindi magkaroon ng espasyo upang ilipat anymore.