What direction is Ultimecia facing at the time? is that even her "real" body that blocks the bullet? She is presumably standing on a platform, unobstructed, nowhere near the throne in which she was sitting nor is the float (or the iron gates, for that matter) visible at all from any angle as the bullet strikes. Note also the brighter flash of light before the bullet strikes, and Ultimicia's previously and later noted ability to teleport in a blue flash...
Additionally, you'll notice as Squall drives up afterward, the back of the float is wide open; blown glass and neon decoration, with intricate, but hardly solid metallic artwork. Nothing solid directly obstructs view nor bullet from a high angle. The only reason it's not obvious to the audience is the abundance of ambient, low-level lighting, which casts the "interior" of the float in shadow, neither of which would have obscured Irvine's view from their positions.
Also, it's a fantasy game... you have people summoning giant monsters and magical fireballs, etc., by effectively shoving those inside their bodies (ew!), not to mention an horrific timetravel/time paradox scenario, absorbing sword blows, magic spells, bullets, and the force of gravity itself wearing nothing more than cloth dresses and leather coats and the occasional magical soda can... and THIS is what breaks your immersion?
Besides... the float clearly turns left and heads down the street in that direction, how did it then become trapped in the gate directly across the plaza from the mansion?
One more thing... you can embed youtube videos by simply typing "youtube=*" in brackets with the video id code (the sequence of letters after "v=" and before any "&" in the video's url) replacing the *.
Thus:
