The interesting part of a standing mirror is not the top, it is the floor. A tall gilded frame carries most of its weight high, so the base has to be drawn before the ornament is.
Our artisans start by striking the tipping line on the drawing board - the line through which the piece would topple if it were pushed. The scrolled feet are then placed so their toes land beyond that line at both front and back, which is why they turn outward rather than tucking under. Only once those two contact points are fixed does the base apron get its shell and its C-scrolls, and the ornament is composed to fill the space the feet have already defined.
The same logic runs upward. The crest is the heaviest single element in the frame, so it is carved from a stock that is hollowed on its back face, taking mass out where nobody sees it and keeping the standing piece calm on its feet. Anyone can carve a shell. Carving one that leaves the mirror steady is the part that takes years.