Another vote for pelican here! Had a 45qt in a bear locker for a week and the ice we put in from our freezer was still in the same shape as when we put it in.
So if your first group hits an inch high at 12 o'clock, second group is an inch out at 1 o'clock, next 3 groups hit at 3 o'clock. Use the middle charge weight of the 3 3 o'clock groups and adjust the seating depth to fiddle with the group size.