You might want to check this out. It pretty much spells it out from the horse’s mouth.
What happened to you was like duck hunting. You were just the unlucky duck. The impeding law refers to moving over if you have a right lane to move over to. It doesn’t give you the permission to speed up, though that might seem the logical thing to do at times. In CA, what you should be most concerned about are points on your license, which go hand in hand with speeding tickets. They can raise insurance, etc., more and cost you more over the years than getting a lawyer and gambling on reducing it. Even if an atty, lowers the fine, the point will still be there.
Your best bet is to go to take the class route (however, you may have already passed that up by requesting a hearing). I have only had one ticket in more years of driving than some people here have been alive, (for getting stuck in a carpool lane and not being able to get out. I had a blind spot in the car and couldn’t get over to the left safely) but took the class and the majority of the people there were there for speeding tickets like yours. The instructor started the class by going around the room and asking people how and where they got their tickets. I learned every speed trap in the
county. Worth what I paid for for the class. Most of them were just after a downhill grade or through towns where the speed limit changed often. I payed a lot more attention to my speed after that.