Joaquin Phoenix Defended by 'Napoleon' Advisor After Brian Cox Critique

Joaquin Phoenix has an ally on the Hollywood battlefield -- the historical advisor from his film, "Napoleon" is leaping to his defense following some biting criticism from Brian Cox.

Lorris Chevalier tells TMZ ... Joaquin did the best with what he was given on-set -- even though he himself wanted to take "Napoleon" in a different, unique, direction ... but he faced stiff opposition.

Despite his ideas being shut down, Lorris says Joaquin really threw himself into the role ... hitting up spots like Napoleon's private castle, the Malmaison and several other Napoleonic sites around Paris for some hands-on character research.

Lorris acknowledges the disappointment behind "Napoleon" is understandable ... but as far as the historical nitpicking goes, the movie was meant to be a visual experience, not a documentary.

At the end of the day, he says his job is to juggle accuracy with storytelling ... and he felt as though he could lean on Joaquin's stellar acting, and Ridley's knack for jaw-dropping visuals to bring Napoleon to life.

As for Brian's claim he could've played Napoleon better than Joaquin -- Lorris says BC could slip into an older version of the emperor's boots, especially since he possesses the same charisma Napoleon did among his soldiers.