It's a perspective effect.
A fixed perspective causes things to appear
smaller when further away, not
lower.
The only case where an object would appear to become lower would be if it was entirely higher than the PoV's vanishing point when it began, while things lower than the PoV's vanishing point appear to rise. Things to the left begin moving right and things to the right begin moving left (seeing a pattern yet?). When travelling in a line parallel to the PoV's line of sight, all objects appear to approach the vanishing point from wherever they are (
they certainly DON'T cross it), and lessen in speed by their apparently closing proximity to it; this causes the effect of objects moving further away appearing to shrink. You lose, roundy.