After buying the 50ppm CYA solution from TFTestkits (used to show 50ppm CYA in the test), I am now able to verify what 50ppm should look like. This would also explain why when testing inside I get about +15ppm higher than if I test outside (in indirect sunlight).
I was using around 2ppm/day (on sunny days) with the solar cover on. Adding up to 3-3.5ppm FC at night when my target was 5. On a sunny day with bathers (w/o cover, obviously) I could use up to 3.5ppm/day.
I've probably been targeting an FC that's 1-3ppm too high the entire time I've been doing BBB. Obviously the CYA test MUST be done outside with indirect sunlight.
I verified using pool calc that my CYA test was close, using last years level and the amount of water replaced when opening. Of course the difference matched up. Which tells me my testing has always been off.
Now I just need a sunny afternoon to test, hopefully tonight or tomorrow. My guess is I will be using far less chlorine from now on.