Odd that they would go wider in the rear for rain setup. All rain setups that I’ve used involve going wider in front (a lot wider) and then setting rear approx same or slightly skinnier than the front. Rear rain rims/tires are also not as wide to begin with, so that makes the rear narrower by default.
In the rain the kart wants to push really hard on turn entry, so the goal is to get the kart to tip easier by using a wide front (lots of mechanical jacking effect) and skinny rear.
I’ll see if I can dig up a good rain setup guide.