ChrisR ah yes, Scottish Power. Was with them once, never again.
To answer your questions, my thought process was as follows:
1) multiple reasons, mainly:
a) using SoC% to trigger an export if you're already below that level, the schedule doesn't run, so if you only have one slot you export nothing.
b) if it does run and you hit the min early, you end up drawing from the grid for the rest of the evening.
2) it's just a calculation based on the max discharge rate and total battery capacity, split in to 30 min slots.
3) in my experience, charging will take priority. In summer, I tend to leave plugging the car in until late evening and try to extend the charging in the morning, finish at say 07:30. Obviously, if the car's charging, you've reduced your export potential.
In the winter (with an ASHP), the more charging slots the merrier.
Hope that helps a little.
