It will work as long as the the shaft is not too long when the 3PT is up high. If the compressed shaft length is too long, you will smash your drive spline back into the tranny and have a huge repair bill.
When you raise the 3PT all the way, lets say the minimum distance is 32" from the tractor to the tiller. But if your compressed shaft is 32.5", you are in trouble.
It doesn't matter when the tiller is down low. The shaft is extending automatically to the correct length back and forth as long as it is long enough. Of course if the longest length is too short, the shaft will come apart. If that happens, you have no repair bill. you merely need to buy a longer shaft.