May,
You’re not in error 🙂 I would suspect that the TEMS during a drivetest is located in a weird place in the car (under the seat, or at least no into a vertical position nearby a window).
a “normal” MS is in a more favorable position.
Try to move the TEMS in your car (but keep watching other cars…), the results are spectacular.
(spectacular, compared to the boring uneventful typical drivetest…. zzzZZzzz)