Ever wonder why some guys still look good with a 18-20mm long philtrum? Because they have a lot of vertical length on their chin, BUT their hairline is also low set, NOT high set. If you have a high set hairline and long philtrum it is death because by vertically lengthening your chin more you will look fucking retarded. Your face will look too long. Your features and facial harmony will be off.
Long philtrum + Vertically long chin + Low hairline = ideal
Long philtrum + Vertically long chin + High hairline = death
Example of Pitt who has a long philtrum, long chin and low hairline:
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Long philtrum and short jaw. Death sentence!