Got the letter from DWP this morning, and I have indeed been put in the support group.
They're backdating SG component, and EDP to 7/10 which is the start of the 14th week of my claim. I phoned them to double check this was correct, after the comments from Gordon, and they said:
You're entitled to EDP because you're in the Support Group, and you weren't in the support group until 7/10, so the EDP starts on that date?
I couldn't really argue against their logic, but it also doesn't sound right, but they were adamant that this is the case.