I never said it was "better" pointing down. I am saying it makes no difference - omni being omni (except maybe at 13,000Hz).
The real issue, before we got sidetracked, was about the Audyssey mic and the way it should be pointed (up) and whether this impacts negatively on an Audyssey calibration of in-ceiling R, L and C speakers due to the mic now being pointed close to directly at the speakers as opposed to at 90 degrees to the (conventional) speakers. I still maintain, based on reports in this thread concerning in-ceiling speakers wrt to Audyssey that Audyssey doesn't do a great job on in-ceiling (main) speakers and that is probably/possibly because of the odd mic orientation wrt to the in-ceiling speakers. It is, and never was, more than a hypothesis though.
Earth to Keith: if, as you say, completely up or down makes NO, as in zero, difference, then how could an omni mike make a difference with ceiling speakers because of an "odd" orientation? I have always, if you look it up, conceded that there would be little, if any, effect in the bass. If you are just as happy having a known dip in your measurement mikes' response centered at 13k or wherever, though that is going to be much lower in frequency and potentially greater in magnitude with the wide flared body of the supplied stock Audyssey mike, then knock yourself out.
I do not mean to overdramatize this, because neither you nor I have seen any measurements of the magnitude and width of this dip with any mike, let alone the mikes we use for measurement. You seem to be working hard, though, at denying and minimizing its presence or significance without any empirical data. Whatever. As for me, if I can orient the mike so that it is even a little tiny bit more linear at some frequencies in picking up useful room reflection information, rather than useless reflections off of a listening chair ( see the sketch artist's diagram you supplied) then, by golly, that is what I am going to do. As I said, it cannot possibly hurt. And, maybe it influences things a bit more than you are stubbornly willing to concede. Who knows? Likely, we will never know for sure.
As a de facto guru in this forum, it's not that you should just be repeating the Audyssey party line about orienting the mike up. But, we now have some documented theoretical evidence of potential mike response issues of perhaps only small importance that help support that view. I do not think you should be going out of your way to deny, minimize or undermine that out of, frankly, what appears to be nothing other than argumentative piqué. Trust me, I am not trying to steal your unofficial guru status from you or challenge it. I am just interested in getting to the truth of the matter, mainly for the sake of other less experienced readers of this forum,
Getting back to the ceiling speaker issue, I feel it is nothing but a tangent. I do not see support for the notion in this forum that it causes special, different or unique measurement problems any more than other configurations, e.g., DSX height speakers. If you wish to waste space and time on it, however, you are, of course free to do so, though you and I both lack any kind of major experience with this kind of configuration. As far as he and I were concerned, the calibration of my brother-in-law's system with ceiling surrounds was just fine, with the mike pointed straight up, of course. Other systems I have done with high wall surrounds were also fine and without incident. I have no clue why you wish to make a fuss about it.