Saddle height is not measured vertically. It's normally measured along the centerline of the seat tube, so most of the setback is always included. The additional saddle setback from the seatpost is never enough to make any appreciable difference in the overall measurement.

If the saddle height is dropped by 25mm, then is should move forward by 7-8mm, since the cosine of a nominal 73 degree STA is .29.