I've been researching Egypt around the 18th kingdom (Akhenaten through Ramsses) and am impressed with PM's rendition of the Egyptian chariot.
The axle rested behind the chariot (as depicted by PM). This made the chariot faster and more mobile (but required it to be lighter and more fragile)(the chariot was faster because with the center of balance so far back, it was less likely to hit a bump and fly forward over the horses--but conversely the horses had to support more of the chariot's weight so the structure had to be lighter).
Hittite chariots, on the other hand, were center-axled (like the Roman chariot) and less maneuverable. The Hittites used their chariots as shock engines so this was "OK". (Egyptian chariots were used like mounted archer platforms, whereas the Hittites, fighting with javelins, used their chariots in melee to a greater degree.
-Tim