I kind of agree with what you're saying. The flatness is NOT a reason to say it isn't a 'Hill Figure'. Perhaps the name for them needs rethinking! It's obvious that the ones on the sides of hills will out-survive the ones made on the flat due to ploughing etc.
>> landcape figures like Nazca lines have to be seen from above
The Nazca lines have been quite convincingly shown to be (ritual) pathways. Each one is a continuous line with no closed loops. They must be totemistic with the tribe walking along the lines and describing the image of their totem animal, which presumably lived in the sky somewhere and could see this being done.
