Another good example is running a red light... I could run a red light at 15 mph, and that'll get me a 21453, or I can run the light at 50mph and that to will get me the same 21453; the officer can make note and make mention of my speed but as long as he's able to articulate that I entered the intersection while facing a red light, he's met the burden of proving my guilt.
In this case, the element that requires proof is whether the defendant was driving in a manner that impeded traffic around him? Clearly, even by his own description, he was. Being thick headed has zero impact on your guilt or innocence.
As far as reliability, credibility, believability... Whatever you take away from the officer, you aren't adding to the defendant...
So the officer starts out with 90% and loses 30%, whereas the defendant starts with 25% and ends up with 25%.