Yes you are correct.
Mana barriers only affect entities that have a true tangible astral form
This include wholly astral subjects (such as spirits, projecting magicians, manifesting magician or spirit etc)
Dual natured subjects (such as vampires, ghouls, materialized spirits, magicians using astral perception)
Active magic (sustained and quickened spells, preparations, activated foci etc)
It means that a magician (or materialized spirit) that is using astral projection while riding an elevator through a mana barrier might get knocked unconscious.
A magician that is not using astral perception while riding an elevator through a mana barrier will never be knocked unconscious.
Riding elevators while using astral perception is dangerous ;-)
You might want to use astral projection to scout the elevator shaft before you do that....
But a magician that is not using astral perception or projection will also be unaware of the mana barrier. Which mean that if he got sustained (or quickened) spells (or active foci or preparations or any other active magic) they will cause astral intersection with the mana barrier as he move through the barrier - and either the barrier will collapse of the spell will end. Or both the barrier will collapse and the spell will end. Depending on the astral intersection test.
To sneak your spells through a barrier you normally need to first be aware of its existence (typically by using astral perception or projection).