I agree!
My idea was one box which is slightly taller than the two smaller boxes, perhaps something close to the black top-right box in this picture:
A simplified version of the face might look like this:
_______
|[=] oo |
| oo oo |
| (O) |
---------
or even this:
_______
| [=] o |
| o o o |
| (O) |
---------
That should be sufficiently visually different from the other two small boxes. The reason I'm pressing for four is that that gives you enough to mix and match them to create different-looking workstations. Or to provide enough visual variation for a big radio bank using multiples of all the boxes. Most examples of early radio operator workstations have many boxes, sometimes as many as a dozen with all sorts of functions - but I don't expect you to make dozens!
I do promise to buy multiples though!