Ah ok, that makes sense about what Min SOC on Grid means.
So I went to create a short Force Charge window and discovered that the battery had been charging at just over 1kW since 19:00 when the previous schedule had expired, despite the "Remaining Time Slots" being set to Self-use!!!

SoC has gone from 12% to 19% at peak rate...
Anyway, I created a three minute Force charge with the settings you suggested and the battery stopped charging during that period!

(Maybe three minutes wasn't enough??)
(Also created a Self-use slot until 23:30 to stop the battery charging during peak rate!)
I'm currently on IOG and Outgoing. Have asked Octopus to move me to Agile Outgoing, but I've never been on IOF.
So - no charging when it's told to Force Charge and charges at ~1kW when there's no schedule set. Confused you will be!! Any ideas what to try next?