Our group don't really need to look at any pattern, just split in groups of 4:
1 tank/1 healer 2 dps go left, same setup goes right side.

1. Find Bahamut position, if you are part of group that is going left, pan your camera directly west(east for group going right) of bahamut not map location so bahamut is your North reference. and start moving on green mark.
2. If twintania is not in in your front view as you go east/west....use Rear view camera to see if directly behind you, if not than your location is safe and keep adjust position so you are not stack with another dps/healer (tank is safe to stack)
If twintania is in front/behind make adjust to avoid the dive, you should still have few secs to spread out once twintania dives.

I think the key is to minimize camera movement and just move directly east/west of bahamut (avoiding bahamut dive) and use rear view to see if twin is behind, this gives plenty of time to spread out/see where everyone is heading for the incoming megaflare/splash dmg.