I'm pretty sure I've been doing it wrong, but I have always treated the chart as linear, although I'm sure it's truly not. So every 2" shorter bow, reduced mass by a half ounce. And then apply the other rules. It's always worked for a 44 in bow you would reduce mass by 3.5 ounces. I built a 40" bow using this method, of course sinew backed, and it came out what seems like an appropriate width and thickness for its poundage. I'm sure someone else knows more about this tho, this is just how I've done it.
Eric