Here is the basic idea behind up firing speakers and some of the issues that may make them less than ideal. Humans locate sound via 3 mechanisms, interaural time differences for low frequencies (large enough to diffract around the head), interaural level differences for high frequencies (those too small to diffract around the head) and head related transfer function. Depending on the angle at which the sound approaches the ears, various notches or peaks in the frequency response appear, this is the primary mechanism by which humans determine side, rear, and overhead sound.
ITD and ILD primarily serves to relay left/right location.
Humans will always focus in on the first wavefront to reach the ears, considering its nearly impossible to make a small Atmos module have such tightly controlled directivity, we will always hear the sound from the speaker first, and the ceiling bounce second. This is why eq is needed, to properly mimic the hrtf of an overhead sound. It's nothing more than a well designed version of "virtual surround", for overhead effects.
I agree it's much better to actually mount speakers above vs using an Atmos module. There's many options for those who can't install in ceiling speakers. In a x.1.4 system, one could mount top front and top rears with goo effects, with a 5.1.2 system, speakers can be mounted on the sidewalls high up, this works better if the room isn't super wide and the ceiling is above 8'.
The other, and obviously best option, is to simply mount regular speakers on the ceiling where you would have otherwise installed in ceiling speakers. If you can swing wall mounts for heights or surrounds, you can easily just mount those same speakers to the ceiling. Speakers with threaded mounting hardware can be attached via an omnimount on the ceiling, this is what I've done using klipsch rb10s. For speakers without mounting hardware, the omnimount can be attached via screws directly into the speaker. One benefit of this setup is that you can use the same speaker line that you use for the LCR and surround, which offers perfect timbre matching.
Sent from my LGMP260 using Tapatalk