Speaker depth is greater than top plate

I think you will be okay, most of the time the top plate is smaller than the bottom of the speaker.

Should be fine. PS: using blue tack: spread it super thin. Hard to do... but it will REALLY make a difference.
Spread it evenly about 1mm thick all around. massage the blue tack a LOT before trying to spread it out helps.
I used it on my B&W 805s and B&W stands. Super!