Numbers and class letters should be positioned next to each other.
From 3.7.b. Not sure if they intended it that way, but next to IMO means next to, not over or under. I might be wrong.
I really can't imagine that if they contrast well and meet the size specs that anyone would ever complain if the class was under/over the number, but I hate to say that with 100% certainty, especially if you mean at Nationals.
If this question is in regards to a national event, you can submit a letter at sebscca.com
If a local question, ask your local tech or T&S people.