This is what I have discovered about ballast fill fill via the BIG.
The ballast fill via the rider settings is based upon time and not the %full of the tank that you will see on the BIG screen. I had an issue where the I set the fill to 50% and it was filling way past that. The dealer service mechanic (good guy) and MC via the dealer were stumbling around figuring out how to correct. The mechanic mentioned that he was told by MC the ballast ran via timer. If you read other posts about ballast you will read how you can adjust the timers - this appears not to be how you do it for systems equiped with BIG. On the BIG, go into System Setup and you will find Ballast Configuration where you can adjust the fill and empty times. I simply lowered my value until the pump ran for the period of time where it hit the % full I had for the rider setting. I feel this will not be the most accurate (running based upon time) but at least I now understand how it works.
I have an 2010 X-15, I don't know how much this applies to others so your mileage may vary.