ESA support group query

I was very surprised when I contacted ATOS to check that the medical questionnaire had been received. I only put on my claim on the 4th february, got the form by the 8th and sent on the 9th.

The job centre had said it was taking much longer than 13 weeks for ATOS to make a decision, yet when I rang ATOS they had already looked at my form and supporting information, put me in the support group without need for a medical and sent it back to DWP for their decision makers to decide.

I am very grateful I found this site as I am sure the support info must have helped. So thank you, I am so relieved!
I only sent some some discharge summaries and extracts from my medical records as I felt bad contacting my doctors/nurses for letters as they are so busy.

I wonder if you could help with a couple of queries. The first is- how often do the decision makers disagree with ATOS?
And the second is, if the decision maker does agree with ATOS and put me in the support group, do I get the increased support group payment straight away or have to wait for the 13 weeks assessment period to finish?

…assuming the DWP can locate the lost medical certificates that were sent by me and have disappeared.