Just always using 100% of range would probally cause all sort of problems. eg when the con gets bumped away slightly.
Additionally tag could be added to control how much closer the builder gets.
well, that would be needed for everything where range is involved.
How close should a unit get to repair? If the repairee moves away, when you should it start to follow?
You do not want it to start/stop all the time either.
Then weapons, how close should you get to fire?
Would need many tags and it would still "fail" in some situations, so it isnt really trivial to find a "works for all mods" thing.
Maybe lua it with Spring.SetUnitMoveGoal or something.