I’d be tempted to attach the speaker brackets to the walls and move them forward out of the alcoves. Many, but not all, speakers like to have some room behind them to improve the soundstage etc.
Actually, on second thought, I would hang them from the ceiling, so I could place them anywhere I wanted. And when you have them mounted as high as you do, make sure you position them upside down. That way the tweeter is closer to your ears, and the woofer will get more of a bass boost from the ceiling and corner.
Cheers.
Dave