P.S.: forgot to add to clarify (2) that the sign shouldn't be related to the response.

Hi, thanks for your reply. Let's see if I can answer properly: (1) The response is luminescence units, an arbitrary intensity variable. (2) The sign of the distance is basically and indication of whether the measure were done in left or right side of the sample. It is a distance in mm in which 0 would be the centre. Thank you very much for your time :)