Well, in that case i'll just do that math to their recommendations.
1. If height of entire photo is 70 mm
2. Chin to crown is 31 to 36 mm
3. Face is centered
Therefore: distance from top to crown = Distance from bottom to chin
Hence:
(70-36)/2 = 17 mm (minimum).... and (70-31)/2 = 19.5mm...