The answer to your question is YES.
You are correct in noting that the response of our instruments is linear. More than that, electrochemical voltametric sensors (such as we use) are inherently linear, with no electronic compensation required.
However, for optimum accuracy in most applications, it is best to calibrate the instruments at a concentration somewhere around 50% of the scale range or higher, if you can. This is because there will always be various sources of error beyond the sensor electrochemistry, and prudent analytical technique would frown on calibrating an instrument at 1% of the scale range for readings at 90% of the scale.
Furthermore, for optimum accuracy, if for some reason you must operate toward the bottom of the range, ideally you should calibrate close to this level.
Saying that, for most customers, calibration at 50% of the range or higher should be quite satisfactory.
For more information, please consult our articles on accuracy and minimum detectability.