You can show him the recommended placement per the AVR manual. Side surround is 90-110 degrees, preferably behind the listener. Beyond that, it's the owner's money and if you won't do it someone else will. Open concept rooms are best suited to having just front speakers so compromises have to be made. Are there high or vaulted ceilings? A ceiling speaker with angled baffles angled towards the main seating area might work better but you can not add ATMOS in that situation.
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