The answer I was once given to this question was that the glidepath angle is non linear. The formula for a M0.73/280IAS descent is
: (((FL-10) * weight) / 17) + 40 = distance from airport. +/- 2nm for each 10kt of wind !!! Weight in tonnes.
From TOD the angle starts above average and by ED it is less than average. Divide by 3 works quite well I find.
I will look at the pitch angle next time I descend as this formula doesn't answer that question.