Section of foot soldiers should be this? (6)

I believe the answer is:

instep

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'section of foot' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for instep that I've seen before include "Arch area of the foot" , "Top of foot" , "Part of foot between toes and ankle" , "Part of foot (how to march!)" , "Set pin in part of foot" .)

I've seen this clue in The Telegraph.

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