Sean, i am not really sure what kind of meter you have , but seems like what you need is a spot meter. The spot meter will give you a 1 degree angle reading , allowing you to achieve a selective reading troghout the entire image. Seems like your meter attachments might have the capabilities to transform you meter in a spot meter, but of course this is only a wild guess.

If time is not an issue , i would also prepare for the shot by going phisically in the far away area of the image and having a thorough reading up close , then going back to the camera and taking the shot. Being nightime you probably won't have shifting of intensity in light .