So I finally figured it out. The reason why I was unable to get to the correct A+ score was because in the mission they have an objective on the side that you can see with your ghost once it starts. Not sure it is random or the same each time. In the last round I played, I rushed through on K1 taking out the scanner/jammers (3), then got to the end boss with tons of time left. I noticed on the left side of my screen when I brought up my ghost that I needed to get 20 precision kills, so I took my time getting head shots which was kind of difficult with a voltshot weapon, but managed to pull it off and had time to spare, too. I received a 5 tier weapon, which was garbage, but a 5-tier none the less. So that was the root of the issue. Someone mentioned Objectives to me and never realized there was an added objective that I could see through my ghost once the level started.