Technically it's one all-purpose 100x100x10 box model with different fpes pointing to different textures. But I made a boxy test building out of them. When I look down it's like the ones acting as the ceiling disappear and let light in but the ones acting as walls do not do this.

This is a video of what happens: https://streamable.com/ti8m8

These were imported manually. But I also tried the GG importer and the same thing happens.

The stock Modular Wall (5) does not do this. So I compared my fpe with its. But what's different doesn't seem like it would cause this. And I don't know how to apply something like physics0 to my fpe. All I know about physics shapes is that they help with collision according to google searches. So my best guess is that it has something to do with my model. But I don't know what.

Does placement of the origin matter? I placed the origin in the corner so it would interlock easily during extraction along the grid. How wide do models need to be? I read a years old thread that they need to be 10 units to block light; is this still true? My original model was 1 unit wide and I'd prefer to do that.

This is my fpe:

;header
desc = Wall 8ft Tile

;visualinfo
textured = tilepc_color.dds
effect = effectbank\reloaded\apbr_basic.fx
castshadow = 0
transparency = 0

;orientation
model = Wall 8ft.x
offx = 0
offy = 0
offz = 0
rotx = 0
roty = 0
rotz = 0
scale = 100
collisionmode = 0
defaultstatic = 1
materialindex = 1
matrixmode = 0
cullmode = 0

;physics shapes
physicscount = 0

;identity details
ischaracter = 0
hasweapon =
isobjective = 0
cantakeweapon = 0

;statistics
strength = 25
explodable = 0
debrisshape = 0

;ai
aimain = default.lua

;spawn
spawnmax = 0
spawndelay = 0
spawnqty = 0

;anim
animmax = 0
anim0 = 0,0
playanimineditor = 0


This is the Modular Wall (5) fpe:

;Saved by FPSCR Object Importer v1.000
;header
desc = Modular Wall (5)

;visualinfo
textured = mod wall_color.dds
effect = effectbank\reloaded\apbr_basic.fx
castshadow = 0
transparency = 0

;orientation
model = modular wall (5).dbo
offx = 0
offy = 0
offz = 0
rotx = 0
roty = 0
rotz = 0
scale = 100
collisionmode = 40
defaultstatic = 1
materialindex = 1
forcesimpleobstacle = 1

;physics shapes
physicscount = 1
physics0 = "0,460.768676758,248.877502441,29.3311386108,1.56192743778,-3.12385487556,0,0,0,0"

;identity details
ischaracter = 0
hasweapon =
isobjective = 1
cantakeweapon = 0

;statistics
strength = 25
explodable = 0
debrisshape = 1

;ai
aiinit = appear.lua
aimain = default.lua
aidestroy = disappear.lua

;spawn
spawnmax = 0
spawndelay = 0
spawnqty = 0

;anim
animmax = 0
anim0 = 0,0