Re: "the monolith is a representation of a wideframe cinema screen rotated 90°."
Nope, sorry. The dimensions of the Monolith are explicitly given as being in the ratio 1:4:9 - the first three square numbers. The ratio of a cinema screen is 2.35:1, not the necessary 2.25:1.
I applaud your pedantry (obvs) but must also point out that 6*9<>42