Isn't that the truth. The last time I sent logs to the mill, we didn't buck anything to 40s. The contractor sent most of it as 24s, a lot of taper.Also, in the past, short logs were favorable to the logger but not the mill. Logs are scaled with a cylinder in mind and the small end is the diameter used. There is taper in trees so a longer log actually provides more "free" wood to the mill.
Our last sale in SW Oregon ALL went as tonnage, which I found surprising. None of it was export size or quality, though. That was as much a rehab sale though, the last time it was logged my grandfather (may have been in my great-uncle's control as he was dying from colon cancer) the contractor didn't replant. About 55 years ago.
And having the logging pay for rehab, replacing poplar with more desirable species sounds like what the OP is trying accomplish.