I find it interesting that Group B (HM) has a five minute window while Group C only has a three minute window. One would think that each progressive group would be larger and therefore would require a larger window of time to start the race.
Based on a few years of data that I have from past runDisney HM events when a 2:15-2:30 corral placement was available, the % of runners was around the same as the <2hr and 2:00-2:15.
Year, sub2, 2:00-2:15, 2:15-2:30
2017, 9.8%, 10.0%, 11.4%
2018, 10.7%, 10.1%, 10.6%
2019, 9.7%, 9.5%, 9.3%
2020, 8.9%, 7.9%, 8.6%
According to their start timing and assuming they're using an even rate distroubuition across the starting line (which they have in the past), we can surmise the approximate % of runners within each corral.
5k - 7.6%, 9.1%, 9.1%, 36.4%, 37.9%
10k - 7.6%, 9.1%, 9.1%, 45.5%, 37.9%
HM - 4.5%, 9.1%, 6.1%, 47%, 33.3%
Based on past runDisney data, these numbers make sense.