On the topic of grade boundaries for edexcel history, my teacher has explained that the A-E grade boundaries will be set at 80%, 70%, 60% of the raw marks (so 160, 140, 120) and so on. The A* could be anywhere above 160 so that around 7% of the cohort get the A*. This could be wrong but I know he works with edexcel very closely so hopefully is passing on the correct information!