EdC; Try this
1. The proper saddle height is when your heel is firmly against the downmost pedal and your leg straight.
2. At this saddle height, the saddle stem should be inside the downtube by a minimum amount. In other words, you don't want the saddle stem to be at the tippy top of the down tube as it would be unstable. The saddle stem should be a few inches inside the downtube in order to create a stable connection.
I believe this length is what Cort is referring to. Often there is a mark on the seat tube indicating the maximum amount you can raise the tube (or the minimum amount that needs to remain in the downtube).
I have also noted that Cort occasionally refers to minimum saddle height when a Thudbuster, or other saddle add-on device, is attached to the saddle which raises the saddle height by a few inches even though the saddle tube itself remains at the lowest point. In other words, the minimum saddle height (the lowest it can go) is raised a few inches by the dimension of the added device.
Hope this helps.
