Not sure if it helps, but here are my config settings for three displays from single quad meshes that work fine. The texture size is the region of the texture, which I just use a dummy for. The camera positions are taken directly from cameras set up close to the displays. I had to flip X and Y as seen below:
[DISPLAY_...]
; General settings
MESHES = Display_A, Display_B, Display_C
REGION_START = 0, 0
REGION_SIZE = 1200, 1200
HIGH_REFRESH_RATE = 0
FLIP_X = 1
FLIP_Y = 1
OUTPUT_ALPHA = 1
OUTPUT_GAMMA = 0.55
OUTPUT_SATURATION = 1.0
OUTPUT_BRIGHTNESS = 5.0
OUTPUT_FISH_EYE = 0.0
OUTPUT_VIGNETTE = 0.0
OUTPUT_CHROMATIC_ABERRATION = 1.0
; Mode settings
MODE = CAMERA
CAMERA_0 = 441.164 ,3.66602 ,180.188
CAMERA_0_TARGET = FOCUSED_CAR
CAMERA_0_UP = 0 ,1 ,0
CAMERA_0_FOV = 50
CAMERA_0_ASPECT_RATIO = 1.652
CAMERA_1 = 312.755 ,2.81151 ,-95.0796
CAMERA_1_TARGET = FOCUSED_CAR
CAMERA_1_UP = 0 ,1 ,0
CAMERA_1_FOV = 50
CAMERA_1_ASPECT_RATIO = 1.652
CAMERA_2 = -1009.72 ,24.3076 ,-59.0965
CAMERA_2_TARGET = FOCUSED_CAR
CAMERA_2_UP = 0 ,1 ,0
CAMERA_2_FOV = 50
CAMERA_2_ASPECT_RATIO = 1.652