Points for Zones:

A multiplier would probably work just fine, depending on how you plan to track it. If people are reporting to you weekly, then the chart on page 1 could be used to assign an activity level.

I imagine the problem begins when a zone changes level. It might be a little more work depending on how you're working this behind the scenes, but if (for example) you're using a spreadsheet program, you could have one row for each pilot at each difficulty level, then a separate row adding everything together for purpose of publication.

Or you could simply drop it as a consideration. Someone in a quieter sector is in less danger, but they have less opportunities as well.