Du Mont never attempted a color wheel demonstration with a Royal Sovereign.
Notice it says "dimensional model". In other words, it is a mock-up to demonstrate scale--period. Unless you believe they cut a hole in the floor for the bottom of the wheel.
That's not to say there isn't an element of truth in that story; actually it's a true story full-stop but for one important detail: Du Mont made their demonstration, complete with its fully intended consequences, on a 20" set. The 30" tube didn't yet exist.