Whereas some people might prefer some kind of speaker anchoring on the top plate, I prefer a simple flat plate that I know will work with any and all bookshelf type speakers

Replaced the small top plate with a larger one3

I cut out a rectangle just slightly smaller than the dimensions of the top plate and it does a fantastic job at securing the speaker

Pay close attention to the dimensions of the top plate (6.5in x 8in) when making your decision.