Rolling average including vacant months as $0? And if that isn't smooth enough, add some smoothing factor, count vacant months as 10% of the last paid value, or

Rolling average including vacant months as $0? And if that isn't smooth enough, add some smoothing factor, count vacant months as 10% of the last paid value, or maybe the first vacant month as 50% with further months decaying. Or some other fancy accounting that makes more sense than the current method.