16'', 18''(<---mine), 20'', 24'', and 28'' I think.
In my opinion, our top bass puts out massive sound when you just tap it, so anything like a 14'' might be too high pitched and would probably transmit sound way more than any other in the line, possibly making it sound like a tick.
And I agree with you about the 28'' being the dark and low tone, but I can see what your director is saying. The sound that the 28'' made, depending on how what the pitch of the head is and how tight it is, could ring forever in the dome.
But don't go listening to me, I'm only a sophmore, I'm sure your director knows what he's doing. So I would trust him.