I recently departed MAN, but my experience may not be the norm because it was the day after The Open. They may have had special procedures in effect because of the extra traffic.

I arrived on the rental car bus and upon entering the building took the escalator immediately to the right on entry. This put me on the ticketing level next to the security entrance. Walking past FlyBe to the left, I arrived at the area you describe where there was a long line to distribute people to kiosks. If you keep walking past that area to the left, you'll find the Business Class / Priority check-in area. This particular day, the line was quite long and not moving. I later discovered this was because the PHL flight was extremely delayed and they were rebooking passengers. I elected to just carry-on my luggage and proceed to security with my mobile boarding pass. This proved to be a great option because the line took forever for some of my colleagues. Only downside to this was I had to answer the security questions upon boarding.