Prepositional adjectives?

In my current conlang, I've opted against prepositions in favor of what seem to
be transitive adjectives (well, not strictly transitive; they can take any of
the obique cases: accusative, genitive, locative, or instrumental) in agreement
with the nouns the phrase describes. Like this:

metto asta celo: si:.
mother-FEM-NOM-SG  beyond-FEM-NOM-SG wall-MASC-LOC-SG is-3S-PRES-INDIC.
"the mother is beyond the wall."
where asta is one of these adjectives which happens to take the locative.

What should I call these? I'm leaning towards "prepositional adjectives", but I
really have no idea.

(For adverbial preposition-type phrases (like "I like to run *in my house*"), I
think I'll use the adjective in the masculine locative singular (the standard
way to form adverbs: remme "swift" > remmo: "swiftly") with its object in the
proper case. If that turns out to be workable)

ever green
sam