The touch would have to be very obvious. In my seminars I teach the monohulls to come so close the bow wave pushes the mark away from them. It is the old "enter wide, exit close" theory that pays off big time at leeward mark roundings.
To a boat following even several boats away might miscontrue this as touching the mark.
At a club race in Sunfish a jerk was half way down the downwind leg and protested me for hitting the leeward mark. No way he could see it, even if I did.