What does the mid-mission Commander XP bar actually represent?

Solution 1:

Actually, this is bar does correlate directly to the Commander XP you gain at the end of the mission.

Depending on how well you day over the course of a single day, you may gain a lot or just a little XP. Whatever you gain is directly added to the level up bar at the end of the mission. In other words, if the total on this daily bar shows +8000 XP, you will gain at least 8000 commander XP when the missions completes - usually more, since most missions don't end at the same time as the daily total. I verified this by going to a low level mission - after one day, this bar showed that I earned 0 XP (since I was too high of a level), and that's exactly what I earned. In another mission, I earned only a couple thousand XP per day, and that's approximately how much I received as a end-of-mission reward.

What's confusing, however, is the progress bar that accompanies the daily XP total. Often it's shown reaching the max, then resetting and growing again. But what happens when the bar reaches full? Based on some testing, think it relates to how many segments will be filled in your main commander XP bar once the mission completes. I checked how many segments I had filled prior to the mission, counted how many times the bar filled up during mission, and verified that I had X number of segments more than I started after the mission.