The Ford dealer is actually right.
The exact position that the temp guage needle points to during normal operation will vary from car to car, depending on variables such as the guage mechanism, the temp sending unit condition, the thermostat's condition, the overall condition of the car's electrical system, etc....
What is important is to watch for variations from what has been determined, in the past, to be normal for each particular car. The "R" is near midrange of the indicated "NORMAL" operating range, therefore the guage is indicating NORMAL temperature range.
For example, my 89 reads between "MA" with a new 180 thermostat and a new sender. Your actual indication will vary.
Steve
89