The question is “why does GF claim to have a 0.5” focal range when the lens only moves 0.4"?
The problem was reported to support: 0.5" focus range not achievable and they claimed black was white.
The machine isn’t physically capable of focusing at 0.5" and it doesn’t position the lens any differently for settings between 0.4" and 0.5". So for 0.5" materials it must be 0.1" out of focus.