Since we're talking cloud absorbers, just what is that? Is it 2" 703 material, or 4" ... or is it 705? How close to the ceiling does the cloud panel have to be? Could there be an 8 inch gap? In fact, could there be a 1 foot gap, say, between the top of the speaker and the panel and a hefty gap between the cloud and ceiling (as long as the lateral position was in the reflection path)? In other words, how low can a cloud be placed? Also, does it need to be rigidly attached to the ceiling or hanging from the corners by rope, for example?
Also, aren't reflections from the desktop potentially more insidious than reflections from the ceiling?
Clouds should cover the point on the ceiling that is midway between your ears and the speakers. Since they're not bass traps, 2 inches is probably adequate, but 3 inches will extend their range to include more of the midrange. They can hang from the ceiling - mine are on chains - and will in fact be more efficient if the gap behind them is at least equal to the thickness of the absorber. I really don't know any reason why an 8" gap should be a problem, other than maybe hitting your head on it when you stand up.
It's true that reflections from the desktop are insidious (good choice of adjective), but they are a bit less of a problem than ceiling reflections simply because the reflection points are closer.
The difference in distance between the reflected and direct paths is what determines the amount of phase shift and how low a frequency they'll cause significant comb filtering at. The lower the frequency, the less likely a given phase shift will cause noticeable comb filtering. The shorter the distance difference, the higher the lowest frequency likely to be adversely affected. Consequently, reflections off the desk or console cause problems at the higher frequencies, while ceiling reflections affect a broad band of frequencies.
Apologies for that last paragraph, it's not the best explanation I've ever written.