Good reasons have been given for why the underslung, (bottom) flap horn is harder to work with. The least of which is related to the flap and which line is the up line. There becomes a real and difficult geometry solution to having the elevator horn now on the top of the elevator. If the stab is moved to a point below the wing centerline, then the problem is non existant, but, now the stab is blanketed in level flight.
I think too much is being made of the possible problem. I've been using the reversed bellcrank for years, and not had an interference problem with the leadouts. The angle that the pushrod has is sufficient to clear the leadouts, esp. if you use a ball link at the bellcrank.
There are several solutions for this, a problem that isn't really a problem, but you run the risk of over complicating the control system.