Joe,

Great experiment. I am assuming that the cylinder you used was, well,
cylindrical. Would not the volume of one inch of wine in the body of the carboy
(say 10 inches in diameter) be significantly more than one inch of wine in the
neck (say 1 inch in diameter)? Thus the change in height would be greatly
multiplied in the neck of a properly topped carboy. All my carboys are filled
at the moment. I will try some experiments in a gallon jug.