If the soil in front of the top part of the stake is weak but the soil behind the bottom part of the stake is strong (e.g. a rock in the way), the stake will not move forward/pivot at the fulcrum in the line of tension (only if it the stake bends under the pressure).
A fulcrum point then can be anywhere along the length of the stake so using a "middle point" as an average position is good in Alamosa's original concept.
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