Thanks for the recent upload of data on the spreadsheet. @GSchmid were all those your settings?
Whoever's settings those are, I found it very interesting that on the same boat as me (2002 SN196 GT40) that you are running KX+, and a high zbox value of 14, and running a much higher ball 1 number then I do. Yet I get consistent times. I have to disclose, though, that most of my timing has been with my wife running 15'off, 30.4,mph inconsistently through the course. I've only been able to run a few skiers through at 32.3mph up though 28'off so my data is limited. Note on the spreadsheet the first listing has now been updated to STOCK PP settings. My listings are lines 14 & 15