Kx does have an effect, it controls how quickly, overall, PP responds. Carb boats vs fuel injected are much different, but individual boats are aslo. Background settings zbx & abc, are there so you can match your settings to your friends Zero Off boat. abc is the adjust for the letters. zbx adjusts the numbers.
If your boat runs away once gps engages a common problem is electrical interference. I has a slightly loose connection n the starter once that created that. Boat would run & start normal but PP would run away once, or shortly after gps engaged.
Another common problem is interference from adjacent wiring. Never "coil" your excess.