From the Gear to Go website:
Originally Posted by Aeroplane
Now, I'm neither endorsing nor contradicting Bill, but trying to understand just what it might mean to be "designed to have the front spindle rotated through the lower half". If there really is something to it, I shouldn't be putting the eccentric into the first quadrant, as you suggest. On the other hand, I'm not sure slippage will necessarily be in the direction of gravity rather than in the direction of loosening the chain - depends on which force is greater. As I am looking at an timing chain in need of tightening with an eccentric right about at 6 o'clock, I'm right at the point of deciding to go with "first quadrant" or trust Bill. As it is a Santana, I'll go with Bill at least for now, although your argument does make me think...
Further, if the builder has done his homework, normal readjustment occurs through the high or low arc of the eccentric and seat height is affected to a minimal degree. Finally, Santana tandems are designed to have the front spindle rotated through the lower half of the rotation--using the upper half raises the captain's center of gravity and decreases stability.