What you have to show isn't that formulaic.
The preponderance of the evidence simply means that they must present evidence of their position that is more likely that not. It isn't like a criminal court hearing, where they have to achieve "beyond a reasonable doubt" which is like 98.9% certainty.
Instead, they have to simply tip the scales in their favor, or you in yours. If it is considered 50.1% likely that their facts are correct rather than yours, that's enough for them to win.
It's really not mathematical like that, but that's just a way to look at it.
So, if they have a witness that says that you were not forthright (meaning that statement of the officer), that's legally enough for them to move forward. It would then be his statement against your statement, but law isn't mathematical. They don't just cancel out his statement because of your statement. The trier of fact can look at the demeanor, believability and testimony of each witness to determine which offered facts seem more likely than not. This is how a single witness can sometimes trump multiple witnesses on the other side....when the multiple witnesses have stories that don't match the facts or line up with each other, while the single witness has a consistent and solid statement of the facts.
So, they have to show, through this one statement, that you did engage in lack of candor. That person's single statement will have to make sense and be believable.
To counter it, your position or statement concerning the facts has to be more believable.