Limited range video on T630

I have libreelec on a HP T630.

Feeding a standard TV (Philips OLED via an HDBaseT matrix) if I set video range 16-235 I get very washed out blacks and a pluge screen clearly shows below black bars to be visible. Setting full range video the pluge test looks correct for dark room viewing (it might crush blacks a little, 1 click up from default brightness in the video settings works better IMO).

Is this expected behaviour. Also is anything being lost increasing the brightness in Kodi (the TV is correctly calibrated for the other sources on the matrix).

Thanks

fishy

All my sources are centralised and switched centrally. The TV is used as a simple HDMI monitor, its internal tuners are never used and its black level has never been set for them (black level is set per HDMI input). The HDBaseT matrix is sending a standardised (1080p SDR TV) EDID to the T630.

There is nothing on the TV to indicate that it recognises it has a PC input (nor would I expect there to be given the above); however one reason for my asking is that the T630 has DisplayPort outputs rather than native HDMI (I use a DisplayPort to HDMI cable).

Thanks

fishy