Greetings Chuck:
The answer to your most excellent question is rather simple: large diameter veneer trees are less common than smaller diameter veneer trees; large diameter veneer trees contain more useable veneer volume and they also contain higher quality veneer due to the fact that large veneer trees have a bigger veneer “quality zone” and thus, they are more coveted by veneer buyers as compared to smaller diameter veneer trees – assuming all other veneer quality attributes are held constant, such as similar color, texture, sapwood, grade, log length, market demand, etc.!
Therefore, large or larger diameter veneer trees – especially black walnut, black cherry, and white oak – generally command higher per unit volume prices compared to per unit volume prices for smaller diameter veneer trees of the same species; assuming all other veneer quality attributes are held constant! This “higher per unit volume price” concept easily goes out the window when you start making apples to oranges comparisons!
I hope this answered your question.