Is the ratio of real thickness to thickness the same? What results do you get for those since there is no point in stretching a polygon unless it is so? And in your case you would only need to calculate the new end of a line in a cumulative manner then use a buffer each segment using a square-end buffer once you have those
ADDENDUM
using numpy to expedite the process and looking at your first four... there is no obvious discernal communality between observed and measured.
a
array([1103, 897, 232, 238])
>>> b
array([1492, 1267, 386, 330])
>>> a/b
array([ 0.739, 0.708, 0.601, 0.721])
>>> b/a
array([ 1.353, 1.412, 1.664, 1.387])
>>> a-b
array([-389, -370, -154, -92])
>>> (a-b)/a
array([-0.353, -0.412, -0.664, -0.387])