Unfortunately none of the above options, I prefer above transition frequency flat direct sound, the slope of the FR at the LP depends on the directivity of the loudspeakers, reverberation characteristics of the room and listening distance.
In my rooms and loudspeakers it is usually around 5dB - 8 dB dropping but also not a straight line drop from 20 to 20000 Hz but usually flat till approximately 500-1000 Hz and then dropping (related to my loudspeakers and room acoustics).