If possible always use the greatest number of teeth to produce your required ratio. For example, 9:27 is better than 8:24, to produce the same ratio of 1:3.
Not quite sure why, but it's bound to be because the teeth must be further spaced apart (less to go around the same circumference) so there is a greater possiblilty of slippage under heavy acceleration, braking or when excess sideways force occurs. One way of solving the sideways bit, is to place washers in the gap between the wheel and the bearing that the teeth of the crown gear are pointing to.
Anyway, long story short. Your were right, but it's not a massive problem as it probably only reduces the life of the crown by 20% or so. So if you need an 8 tooth, then use it. But if you can get away with a 9 or even 10, then use them instead, but change the crown gear accordingly.
Hope this helps.
PS. Waiting for Fergy or Graham to come up with the real scientific explanation for this...