O. Reg 577
It is 1 1/2 inches in diameter or less where tarping is required, but there's about a dozen exceptions/limits/etc. Take a look... If you have some sort of proof that it was 4-6 inches diameter, you should (if I'm reading O. Reg 577 correctly) you should be able to get it dismissed.
http://www.OntarioTicket.com OR http://www.OHTA.ca