I have a 6103 in the bedroom and the semi-glossy screen has a hard time fighting off light reflections (might be the same with the 6303). Keep ambient light low and check your gamma settings... you may need to increase it.
HDR definition for my 6103 presented a darker picture (bec of a higher contrast presentation). Just increase the brighrness level and gamma by one point and lower your lights.
This may help.