the length of your top link needs to be set to the correct length of the impliment in question to accomplish the task at hand.
for example, on a traditional rear pto snowblower you shorten the top link to cut into the snow as much as you want too much and you risk damaging a soft black top driveway, not enough and snow will be left behind, and if you go over board and shorten too much the cutting can stop, etc.... needs to be set to get job done correctly. Of course if you are using an inverted snowblower than setting could be different.
another example is for a logging winch. Top link too short and the tail will not bite in. Too long and front end of tractor can become too light. Of course this all depends and changes when you go from very soft ground like sand to say a clay base.
so yes the top link length is highly variable based on the equipment being used and the circumstances being used in.
height will change as the lift arms move through their range.
cheers
edit: ooppss... me bad.... didn't see this was a quick hitch question.