Here is a nice blog about the subject of Raphia elephant experiences:
https://www.sciencenews.org/blog/wild-things/after-2000-years-ptolemys-war-elephants-are-revealedMy theory is that whatever the species the Ptolemaic elephants on the left wing were outnumbered three to two by the best elephants on the Seleucid side. That may be the strongest reason why the Ptolemaic screen was overrun. On the other wing the odds were not as stacked against the Ptolemaic beasts which held off their opponents- so size or type made no difference.
One other thing- Savannah elephants in modern times are more tame able than used to be thought. But there is a limit- juvenile male elephants will bond with their handlers - but as soon as they reach full size they must be sent off as they are too dangerous to the handlers and people.
So the Ptolemaic hunters probably knew to collect younger elephants to ship up to Egypt. One option is that these juvenile elephants were no match for older veteran Asian elephants which may have been bigger.
Polybius probably only ever saw elephants in Roman armies. These were from Numidia.
One thing remains true- war elephants look cool.