ramjet falls from a position, ramjet activates, ramjet returns to a position and then repeats.
or
what say the ramjet is pushed from b platform at a position, ramjet activates, ramjet is pushed back to a position / b platform.
The scramjet will not hover, instead it will attempt to remain in a fixed altitude. It will do that by going up and down, if you imagine some sort of fixed unmovable object from when it is at pos a. When it falls from pos a it is now away from the unmovable object. Take the unmovable object and see it as the hover height.