For info, Canyon has replaced the Stack+/Reach+ geometry parameters on the new Aeroad geometry chart, for Effective stack and Effective reach.
According to Canyon, they are:
Vertical/Horizontal distance between the bottom bracket and the hand position
For context, Stack+/Reach+ were measured from the BB to the top of the "tops" position on the handlebar.
It is not very clear to me what point Canyon considers for "hand position", but by comparing the old and new system, it is somewhere on the hood – from the drawing, it appears to be the start of the hood cover.
by mtcerio