All that does is increase party dexterity, which actually just makes UPS even lower, which doesn't fix the equation at all. I'm 99% sure the one you've listed is incorrect, I've put it in a
spreadsheet if you want to see for yourself.
As I've said, I've tried messing around with the equation and nothing I've done makes it seem close to accurate. Regardless of the value of Party Dexterity, the Dexterity of the character being calculated for has WAY too much weight on UPS. I've been able to come up with my own approximation of what the real ATB Formula should be (see below, also have a
spreadsheet for it), but I'd like to be using the actual one.
UPS/30 = BattleSpeed + Dexterty * 5
Dexterity = 50
Config Battle Speed = 127.
Battlespeed = 32768/(Config Battle Speed* 960/256 + 120) * 3 * [1-Slow, 2-Normal, 4-Haste] = 329.7
therefore, UPS/30 = 329.7 + 50 *5 = 579.7
Time to Full = 65535/(579.7*30) = 3.8s
This equation is within +/- 0.5s of the real equation for all valid values of Dexterity, Config Battle Speed and the Slow/Normal/Haste modifer in any combination. Still would be nice to have the real one though.