Vertical levels are weird. Think of the top 2 screens as 2 normal screens side by side. That would mean that, on screen 0 (on the top) the BG and FG initial position should be zero. and that, in the middle, 60, and the botton of screen 01, C0. And the pattrn continues.
Also, sometimes the game is weird about what screens dont give garbage GFX.

<TLMB> I use YY-CHR to edit DNA