Terrain not being lit on the +x axis

Hi,

I'm making a night driving prototype and the spotlight acting as my car's headlight refuses to light my terrain on the +x axis. Here's how it looks:

My headlights are moving properly with the car's chassis (they're parented) but only casts light on terrain on the -x axis, not the +x. On the screencap, if I turn the car so it aligns with the +x axis, no light is visible on the terrain. If I align with -x, the spotlight works properly.

I've tried countless parameter tweaks so it would work but the only thing that fixes it is displaying the base map distance at 0 on the terrain parameters. Problem is the texture then obviously disappears and I'm left with a plain green color. Said texture is a regular RGBA grass texture with a plain grey alpha channel.

Does anyone know why would this happen?