Cessna most likely determined the position by empirical means. It probably was some variation of mounting it on the leading edge and moving it around until they got consistant performance at stall.
I do remember from over 40 years ago that it was part of the preflight to turn on the master switch and push the little tab upwards to chech for reeedom of movement and that the stall warning horn was functioning.
In models the onset of stall is usually more rapid as the operate in lower Reynolds numbers and lower levels of inertia.