I would start off with a few hard cover books. As you change the height, you change the sound. Find a height that makes them sound the best for you first before making something.

From what you wrote, it appears you are coming up with a number for aesthetic purposes, rather than acoustic.

Anthem: AVM60, Fosi DAC-Q5
Axiom: ADA1500, LFR1100 Actiive, QS8, EP500, M3, M3comp, M5