My surrounds have terribly poor placement, where for 1 of the then couch is nearly under the speaker which is mounted about 6ft up, so vertical off-axis is hugely important.
Have you considered ceiling mounts, or even aimable in-ceiling speakers like the Revel C763L that are used for Atmos mastering? It's fairly commonly done for surrounds. I actually suspect you can get away with that even with actual Tops, since the Top locations are entirely different(at least for X.X.4)