@hifiman5 The sand box I'm referring to is actually almost identical to the the height of spikes. Bright Star audio made these sand boxes (mainly for equipment), but could be used for speakers too. You don't need the spikes, so it's not like doubling up on the height. You mainly have to customize them for your speakers since every speaker is different size nowadays. Thus, you can make them any height you want.
Also remember, that even if you double the height or it's 1-2 inches different than a spike, it's not any different than other things you have to manage if your speakers are super sensitive by a couple inches to dispersion. Chairs/couches/etc aren't all at the same height. The cushions aren't the same tension. People aren't the same weight and height. Some people slouch when seated and others don't. Thus, the size of the custom sand base you make is virtually immaterial to other things if you have speakers with very sensitive/poor dispersion. As long as you don't do anything crazy with the height of your custom sand base, you should be fine.
It's also a good time to say that I only use large line source ribbon/planar speakers (Wisdom Audio, Maggies, etc). I'm not a big fan of any point source loudspeakers that have all these hyper sensitive dispersion issues, but that's a discussion for another topic and for more reasons than just dispersion characteristics.
