When the FC level stays exactly the same evening and next morning, or only drops by 0.5 (or even 1.0), then the FC level has held overnight. You are getting close, but are not quite there yet. You probably only need one more night at shock level, though it might be longer.
Also, keep in mind that while covering the pool does dramatically reduce the amount of chlorine lost to sunlight, it also slows the breakdown of CC. CC breaks down more quickly when the pool is exposed to direct sunlight and fresh air.
Also, keep in mind that while covering the pool does dramatically reduce the amount of chlorine lost to sunlight, it also slows the breakdown of CC. CC breaks down more quickly when the pool is exposed to direct sunlight and fresh air.