I'm struggling to understand how the activity planner schedules in activities. As per the below suggestion I set the service level allowance to drop by 5%

"For MUST-have activities, you might find a custom impact that allows the service goal to go slightly under your lowest threshold works best.

• default = allow service goal to be reduced by 10%
• MUST-have = allow service goal to be reduced by 20%

For NICE to have activities, you might find a custom impact that uses a tighter service goal range provides better overall results. 

• default = allow service goal to be reduced by 10%
•  NICE to have = allow service goal to be reduced by 5%"

However I found it doesn't seem to schedule the activities where there looks to be more availability/higher SL% achieved. In the below screen shot you can see it's scheduled in an activity (in green) - where the adjusted difference with shrinkage shows as -9 and the SL%'s are also showing lower in this interval than others. Why did it schedule it there? I'm struggling to understand why it's chosen that interval when others look a better option!