Dan: It is important to remember, too, that the primary skills Welles brought to the Movies were from the Theater and Radio, in both of which he was an American innovator. In the Theater, he had emphasized simplicity of scenic presentation (made famous by his friend Thornton Wilder in Our Town), and in Radio, he had used microphone placement and sound levels to establish dramatic and emotional distance. Light and dark, high and low, to zero in on what he wished an audience to concentrate upon, to experience.
And so, in the famous screening room "test" sequence, as mido505, suggests, while he would not want actors recognized he would use later in the film, he also did not care if they were seen or not because they were not important as individuals to the dramatic, emotional and intellectual effect of his presentation. None of these "little people," these "underlings," counted as real human beings as they fulfilled their roles of "yes men." Only Mr. Rawlston (Philip van Zant), in a typical Wellsian recognition of the essential fascism in American corporate life, was to be seen in the spotlight of the movie projector, only Rawlston's voice (and at a respectful level, Thompson's) was of any importance.
I think it fair to say that Welles would have been satisfied if the entire screen had been pitch black with only Rawlston looming up in the light, the underlings, like so many motes, in the projector's beam. Only Rawlston's voice booming out with bored cynicism his orders. Nobody really counted but the Leader, the Decider.
[A character named Rawlston immediately reminded me as a boy, in 1941, when I first saw CITIZEN KANE, of Rawlston's Cereals, which were among the biggest sponsors of children's serials on Radio at the time: "When it's roundup time in Texas . . ." Putting all of us "little doggies" into the corral, to wait for our Hero Tom Mix. Straight Shooter Mix took care of everything, and if you sent in enough boxtops, you got mailed to you a photo of Tom and his horse, framed by "silver rope," which sat on our piano top for years.]
[And you know, most of these recognition problems in "the screening room sequence" can be solved by simply bringing up the black level, adjusting downward the "light" on your TV controls. Your TV will function better and longer, if you do!]