How to increase maximum render target resolution

I’m working with raymarched volume textures, and trying to push the resolution as far as possible.

I’ve increased the maximum texture resolution in engine to 16K using the config file and having no problems importing and using 16K textures in my shaders. But I’m hoping to use render targets as part of the process and would like them to be 16K also.

However when I try to change the resolution of a render target to be 16K it resets it to 8K.

Is there another config setting or cvar that needs to be set somewhere? Or is there some other reason why the render target resolution caps out at 8K even when maximum texture resolution is set to 16K elsewhere?