@waris
Understand that you have a 3.1 setup and now would be adding OWM3 as surrounds. Given the room specs, I think you can consider one of these options. Ideal height of mounting speakers would be 4 to 5 feet from the ground but less that 6 feet. Would recommend the side walls.
After this I guess you want to procure 2 more speakers to be used for Atmos effect. Besides getting in Ceiling speakers which are tall in terms of their housing case, why not look at getting 2 way / 3 way Car Audio speakers? You can check the specs and accordingly get the best ones which can fit in the false ceiling. Car speakers are lighter and being used for Atmos effects would do. Let the sub and main speakers handle all the low bass frequencies. See if this is doable!
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