The problem with elephants is IMHO not that they can stand up to so much abuse but that there are so many of them.

I like to have two units of elephants because if you send one unit in to follow the other it seems to give mutual morale support like regular units as they plow through the lines. However even with a modest two elephant units out of an 20 unit army then the amount of elephant are out of all proportion to the troops you bring along. Most armies of the day were hard pressed to have more then 40 elephants while fielding armies of tens of thousands.
I can field nearly 4000 men and still get about that number of elephants. Meaning that the elephant units are scaled differently then the other troops.

If you halve the number of elephants per unit they will receive a more concentrated missile bombardment leading to quicker deaths/panick/routs while still giving the impression these are beasts with thick hides . It also lessens the speed at which they cut through melee units which I think is overmodelled. And this way they don't get weakened versus melee because elephants are always outnumbered, the limit typically being how many troops can stand around an elephant, which ofcourse doesn't change.

IMHO a neat fix which not only improves gameplay but is historicly accurate aswell.