No it's an actual and effective 75mm stem, current pads are in the middle, but when I measured reach I was at something like 515 (going off of memory) with slammed base bar. My stack is high due to poor flexibility (I have multiple spine fusions from broken back a few years ago) Slammed base bar on the alpha has a min 525 reach based on your chart, which is where I got the 1 cm.

Again, going off of memory from when I measured a few months ago. User error is possible.