Actually, if you raise your CYA to the recommended levels you will find that you can turn the output of the cell down....not up! Both PoolPilot Systems and Goldline Controls have said that the reason for the high CYA levels is more or less because of the way the chlorine is introduced into the pool at extremely high concentration in a small volume of water within the cell. It would appear that the best guess chart does not apply to SWGs for this reason since most of the people on this forum, including myself, report very good results with the CYA in the recommended range and FC levels of around 3 ppm. BTW, DO NOT go below 2 ppm. This has noththing to do with SWG but has to do with the necessary levels of chlorine needed to kill waterborne pathogens based on recent studies!
I myself was skeptical about running the high CYA levels with my SWG at first but found that the unit actually operated better with a more constant chlorine level and at a lower power setting then whem my CYA was at about 40-50 ppm!