Mine touches the string but ive heard some people say it should be slightly short of the string I dont know if its that critical although I used to have mine off the string and it seemed to wear down really fast
I looked at all 3 of my bows and the string is on the suppressor at rest. 3 different bows from 3 different companies.
Hoyt recommends that the string is slightly off of the string at a resting position. You can adjust to find the way that you like it the best.
Which one are you looking at? If you're going with an aftermarket suppressor I'd recommend the String Tamer II from Norway Industries. It is cut to size, but leaves room for adjusment as long as you don't cut it too short. I had one on my Diamond Marquis and loved it. As for the measurement, it's taken from the rear stabilizer hole to the string.