I understand the logic underlying your question but, as PP flag, there are other issues - like availability/location/expense of any first year accommodation (which can vary wildly and for which there is more discernible info). This could be a potentially more important 'tie-breaker' if that is what DC are looking for to help decide.
Obviously there are other potentially crucial factors like course structure, general uni and city vib etc but I assuming your DC has already factored those aspects in prior to selecting their 'five'.
A point to ponder is the gap between their likely performance and the insurance offers (typically AAB is this case?) may mean that the concern about needing leniency is potentially unfounded. For example, if they are realistically projected to hit Astar, A, A, then they can potentially drop two grades and still achieve their insurance offer.
If there is concern one grade might hit C (eg maths) then the focus should be on really working on that one between now and the summer. Ultimately they need to see themselves enjoying their time at their insurance choice, if it came to that.
As others have done, my DC did track clearing activity in their chosen subject areas one or more years prior to their application year but it has been a topsy-turvy couple of years and clearing activity did not always 'repeat'. Better to be 'clearing ready' - in terms of mindset and prior research - if missing grades is a realistic concern.