It’s hard to tell from the pics but you make sense by saying they’re wouldn’t be enough separation from the sides.
For the sides, yeah you want them at or just above ear height. For pre Atmos systems higher was better, like maybe 6’ but Atmos changed that. Plus! For legacy tracks, DSU and DTSnx are great for giving an immersive experience.
So the guy from the store was right, but outdated.