I consider a sling the length of an arm short.
The authenthic Balearic sling I received from Mr Livermore is this size.
I consider a sling the distance between your hand and the feet medium
And a long sling 1 meter +
So for me it would be, plus minus, respectively 60, 80, 100 cm.
So for each person it can vary. A sling is adjusted to the slinger. Ideally you carry three slings for the different tasks, for short, medium and long distances. I do notice each size being good at their task.
But that is what is nice about slinging. Even with 3 slings you are still very light and mobile.