Bern Oulli,
Just out of interest I wonder why it is taught that way. I think most pilots would agree that by the time the base leg turn has been made the descent profile has prety much happend, and range checks are becoming less important, similarly i see little point in giving a range check once the pilot is established (although many of my colleagues do) as the pilot should now be receiving the DME and will know far more accurately (radar being history) how far he has to go than i can tell him.
Personally I will give a range check as soon as possible after first contact on approach and again about 20 nm from touchdown; i may give further checks if i think the a/c is flying an "inappropriate" descent profile.
But quite often the answer to "how many track miles" is " how many do you want"!!!