You can move the lyrics up or down on a stave with a boundary offset which is good.
But if you layer that stave with another and put the boundary offset on the second stave it still moves the lyrics on the first stave. This is not good.
The song I'm working on (SATB on four staves layered into two) has most of the lyrics in the middle, but at one point there are alternate lyrics in the bass (below the stave) and on the next system alternate lyrics for the sopranos (above the stave) and they clash. So I thought I could change the boundary of the alto or tenor to separate them, but it just doesn't work!
If the bass lyrics clash with the soprano lyrics, they're on different systems.
I think that can't be changed with a boundary offset.
Maybe you can solve it with the insert of a page break to have less systems on one page?
Be sure that the option 'Justify printed systems vertically' is checked.