cal,
I think you're overthinking it. Nothing wrong with questioning tradition, but in this case it's just a couple of chunks. Besides, are you going to test your wood each time, as the humidity will vary with the seasons.
Sure the weight would matter, and the humidity (REAL wet) would just smoulder. But...
The difference between one chunk and another, given a different humidity, wouldn't really show an effect given the small wood size.
If you were burning a bunch of logs for BTU's it might and you'll put off more gray smoke (bad) than clear/blue smoke, but not in a cooker this small.
The only think I would do it get a scale and weigh them. There are different densities, but it's really more art than science, you just need to know relative amounts.
Less would be say one or two chunks
Average would be say three or four
Heavy would be more than five.
But in the end in ONLY matters the amount you need for your taste buds.
Keep notes of how much wood and how much flavor you get for your own effects.
The other variables I think are more important (meat, seasoning, sauce, etc) in the end, I don't think most people can taste the "flavor" of a particular wood.