Mounting Sonos Arc above TV (Samsung S90C)

Getting built-in cabinets/shelving so the TV unfortunately will be mounted above the fireplace. I've purchased the MantelMount mm815 so we can lower it closer to eye level when in use, but am thinking about mounting the arc above the tv instead of below. This way I can mount the tv lower and don't have to worry about blocking the upfiring speakers. What are the downsides to mounting the speaker above the tv? I've included an AI mockup of what this would look like when in "storage mode"