The best way to get a jet to turn is to figure out what pin angle it like to be at...
Sort of like caster and camber in a circle car....
You can make a jetboat turn like it is tied to a post, but it takes some experimenting.
With a fixed nozzle, it is nearly impossible to get the setup right. I have a berkeley Droop that has been heavily modified to accept different bushings for different pin angles, I really have not had a opportunity to dick with it much and the guy I got it from has been gone for 10 years or better.

I always wanted to build a nozzle that could accept a steering action input and be adjustable on the fly, but never had the time.
Think of it like trying to make an aggressive turn with the nozzle all the way up, versus all the way down, it will bury the ass if all the way up and bowsteer like a MOFO if all the way down..., there is a balance, but it is tuff to find and will vary at different tracks at different speeds...
I believe the rule is there in case of an engine shut down, it may help steer the powerless craft out of harms way, I betting it wont, but I think that is why the rule exists
GT