Good question, Brad. The DRs absolutely need to be aimed carefully in the vertical direction, the best sound will be orthogonal to the midpoint of the tweeter array. I have never seen a horizontal off axis graph for a DR200 save for this one:
I would imagine that some horizontal aiming of L/R could be of benefit, but without more off-axis measurements (5 to 10deg increments), one cannot be sure.
DR280, being wider, would probably begin to have the drop in off axis spl at a lower freq, but it is designed as a 'longer throw' cab.
You up for off-axis measurements of a DR, MK?
PS - I have my L/R crossover at 200Hz, and my THT mouths are just below and to the right of my L/R speakers. All other speakers cross in at 110Hz.