Via google search no promise of accuracy:
http://www.geocities.co.jp/Playtown-.../manacalc.html
It does depend heavily on level at least in classic there was an upgrade roughly every 5 levels to mana per stat point of Int/Wis capping at 12 by level 60. Plus a tiny base value that upgraded with every level.
From my vague memories of Classic era EQ, the main discrepancy between p1999 and classic is that Int/Wis over 200 gives half the mana per point as 1-200. Classic originally only gave you a single point of mana from 201-255. The dimished returns was added I think in Luclin, more correctly I think it ignored every even point after 201. The only discrepancy between hybrid and caster mana pools other then obvious gear availability choices or preferences was that hybrids did not receive the final upgrade to mana per point at level cap of 60. In other words hybrids received 11 mana per point before 201 compared to casters 12 mana.
I don’t know if that continued into Luclin era or was changed or was ever implemented on p1999 but I doubt it.