Imo it would be worth charging to a point, you want to have some cheaper power stored that can be used in the event the weather isn't very good.
Also doesn't make a ton of sense to charge/discharge the batteries a lot more than needed, if export to grid is the main goal.
The scenarios would vary for each of us I think, I'd probably just charge as much as I can, but ideally I'd have a 2nd charge window that prevented it dropping below say 50% before 16:00, which gives some room for solar to power the batteries whilst also maintaining a SOC that can handle demand in the peak time.
I still want to see more details on what this GE specific tariff is like, because that may well beat Flux/Go depending how it's done.