I was looking for. The 25th was the optimal compromise. I'm learning to play "flatter" around the 2:30 to 2:45 position where the 25th balences out. ). At the low frequescies we play in, i think the mass of the headstock is going to play a large role in how the base frequency and overtones (= energy) are sustained within the string and not lost though transmision to the neck and body. IIRC I remember reading somewhere that the lower the frequency is, the more energy can be transfered. (Anyone who knows about physics please correct me). If this is true the heavier headstock will allow the string to retain more energy at a lower frequency before the "string dynamics" (There is probably a real term for what I mean) cause the stings movments to move though the hamonic overtones (think of the sting moving from vibratong along it entire length to each flageoletto to understand what I mean). The result of this is a sound that retains more low end "umph" and sounds "growlier" with a heavier headstock. 
You know I've actually been putting alot of though into this. The reason was simple, the Basses that I liked the sound of where not the basses that where most comfortable. I learned on a cheep Korien Bass that had a small, light headstock. It did not sound too bad but the great thing about it was it was perfectly balanced for my playing position. I think I need to explain what I mean by perfectly balanced... I (used) to play with the bass neck pointing at the 2:00 position when you looking at me. When I started looking for a replacement (and I looked at many brands) it seemed that all of the basses that where really well balanced in my playing position did not have the "Balls"
Now please bear in mind I am an IT geek, not physics professor but I believe what is acualy ancoring the sting at the tuner end is not only the stiffness of the neck and the force of the neck rod compensating that, but also the wieght of the headstock. As newton taught us, mass at rest want to stay that way (like me when my butt hits the couch.. it wants to stay there
The question is... does any of this make sense or am I way out there? I am just trying to put reson behind my observations.
-Matt
