Which preposition to use with emplaced

behind Occurrences 1%

A maxim carefully emplaced behind sandbags in the trench replied with a storm of bullets, but it was a poor job, firing at an enemy who were quite invisible, and a feeling of slight depression had begun to settle on the occupants of the trench.

on Occurrences 1%

Some mascots, eh?" On our way back to the general's headquarters we must have passed other batteries hidden from sight only a stone's throw away; and yet in an illustrated paper recently I saw a drawing of some guns emplaced on the crest of a bare hill, naked to all the batteries of the enemy, but engaged in destroying all the enemy's batteries, according to the account.

Which preposition to use with  emplaced