[ N II ]  emission line (in black) superposed to the [ S II ]  emission line (in red) derived from the fit model for NGC 4143. We indicate the velocities at different percentiles of the total line flux (5%, 10% and 30%, 70%, 90%, and 95%). The green triangle represent the ratio measured from the ground. In the bottom panel, we report the median of the R_{[ N II / [ S II ]} ratio for all the LINERs in the wings, normalized to the values observed from the ground. This is compared with the median radius of the emitting region, based on the assumption of Keplerian rotation.