FFVII Ultimate weapons

Currently on another (and possibly my last) FFVII playthrough.

Just a quick(ish) question. The ultimate weapons- what are the deciding factors for how much damage they dish out? For example, Cloud's Ultima weapon depends upon his own HP levels, whereas Aeris' Princess Guard depends on whether allies are alive or not.

I really haven't been able to work out how the damage from Barret's Missing Score is calculated.

Cheers

I just think Barrets missing score depends on his strength but Vincent`s Death penalty depends on how many enemies he`s killed. and Tifa`s depends on how much her limit break is full.

I think tifa gets charged every time she scores a miss in her limit break.

Barret's ultimate weapon's strength increases with the more AP materia has on it in the weapon's slots.