The GO tariff is an artificial price (based on octopus' calculated averages). Agile is more representative of the wholesale prices (what octopus actually pays for the electricity).
You can see the agile prices here
https://www.octopriceuk.app/agile
What I imagine they would do is activate your charge at the cheapest wholesale time of the night (which should correspond to the cheapest agile time). That way they will maximise their profit.