5. The following initialization is also necessary after the CPU is reset.
[I] Write the transparency character (e.g. 0020H) into the VRAM
address 0 to 3FH.
 Write OOOOH into VRAM address 8200H.
8. When the vertical reduction ratio of a 3D-LINE SPRITE is set to a value other
than OFFH, the characters which are addressed by 1EH and 20H of that 3D-LINE
SPRITE need to be transparent characters. Or, put a transparent dot in the
locations one dot below IEH and one dot above 20H.
Page 11 Neo Geo Hardware reference
What is the reason for both of these measures? Thank you