The point is not that «عَلَى» must always be metaphorical. In this example it does not express literal physical elevation; a spatial relation is transferred into a nonspatial one.
Analysis proceeds in two stages: resemblance between steadfast guidance and secure elevation, then use of the preposition’s relational meaning for that state.
Particles express relationships with other words. Their rhetorical effect must therefore be examined in the complete construction, not through a dictionary gloss alone.