Maybe the importance level of the first and last task in each group could be manually adjusted and then the user would have the option of having the importance level of the remaining tasks in the group automatically distributed evenly between the importance levels assigned to those first and last tasks.
Maybe the importance level of the first and last task in each group could be manually adjusted and then the user would have the option of having the importance level of the remaining tasks in the group automatically distributed evenly between the importance levels assigned to those first and last tasks.