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Would 'close to eye height' would mean little or no shadow detail at the road surface and a consequential loss of depth perception?
I know coal mining and cycling are different, but helmet mounted lamps (close to eye height) seemed to coincide with tripping over obstacles and tool/working errors, whereas a hand held lamp (waist height when walking, held by an apprentice for other work) seemed to allow better judgement of distance and uneven ground.
Worked in the dark too much, tend not to cycle at night by choice...
Closer to eye height is better for your main light. They're alright for a 2nd light. If you put a strong light on there the angle will dazzle and carry long shadows and scare small children.
If your main light is on your dropbars it can get obscured at certain angles by your hoods+hands. A light on the fork crown or leg can be seen from those angles through the wheel.