An FX sensor is 1.5 inches long. As you worked out at 1X magnification the image is recorded at 1.5 inches long.
O.1x is one tenth life-size and the FX image is recorded as 15 inches long.
A DX sensor is 1 inch long making 1x 1 inch long and 0.1x 10 inches long.
Many problems turn out to be a lack of intimate knowledge of complex modern camera equipment.