We successfully clean WS flux on 1mm and 1.25mm pitch BGA. For 0.8mm pitch BGA, we use no clean, because we cannot remove the flux residue from under them efficiently.
Use ion chromatography testing to be sure it is clean under the BGA. IC is the only way to be sure you can clean sufficiently.
As a down & dirty method for determining capability of cleaners: * Make some glass [heat resistant tempered glass] slugs that are bigger than the BGA you plan to clean. * Glue several BGA to glass slugs at different stand-off heights. * Squirt colored flux beneath the slug. * Send BGA/slug through a reflow oven to bake the flux. * Clean the glass plate. * Inspect the slug after it comes out of your cleaner. That'll show you without a doubt, the capability of your cleaner.