Can I increase the Light Map Coord Index size?

I am creating currently the equivalent of Lego so that in-game building can be created easily with templated pieces, however going above 5 separate objects has led to all new objects to be locked at ‘4’ on the Light Map Coordinate Index. This is causing black objects when I build the scene.

Is there a way around this or a method of fixing it? I personally would have imagined that LMCI would be a 1D array so is there a way to increase the size of this, at least, metaphorical array?