The ear's sensitivity to SPL and distortion both peak at 3.5 to 4 kHz. So imho you really don't want to screw up that region. Now it's not so much that you can't get away with a crossover in that region - not at all. It's that you can't get away with a mediocre crossover in that region.
I don't see how something as narrow as a ribbon could give you the kind of radiation pattern control you'd need to benefit from a Geddes-esque 45 degree toe-in. I think makes sense to just resign yourself to treating that early nearsidewall reflection, which isn't the end of the world.
Duke