Concentric within 3/16"? Really? How the heck do you pull that off? The adjustment would have to be made at the rear most hanger right? The trumpets have to be in alignment or they will not be level.
It's a deceptive dimension. Whatever extension length the trumpet is, it must be centered with a tolerence of 3/16 of an inch. That means if the "gap"is 1/2 inch, or 5/8 inch, or 3/4 inch, it must within 3/16 all the way around.
(Mentally picture a 4 inch diameter funnel
centered in a 3 inch diameter pipe, now move it up or down.)
How you do that is moving the tip in and out and moving the brackets up and down (final adjustment with a 4 pound sledge hammer).
Jim