Something came across my mind for you to research and report back on with angling speaker, and that is if there is any increased audible comb filtering issue. The very high intensity of smaller holes with this weave is designed to move comb filtering into much higher frequencies where we won't notice. My guess is it it will be totally fine, but always better to know for sure. Here's a small portion from the Seymour site:
"For example, any fabric with holes will comb filter to a measureable degree, but in order for it not to have an audible effect the lobing needs to be as closely spaced as possible (our hearing will average frequency/special response) and at the highest frequencies".
However, like I said before, maybe even multiple times, I don't think even a foot higher for your speaker will create much audible issue at your double digit feet distance. I mean, I don't complain when I'm one foot off-center from center speaker in the horizontal sense from double digit feet away, and that's with the ubiquitous mtm.
As for the arguments for placing speakers outside vs inside screen. One argument would be the following, and I'll quote the Seymour site again (and out of order on purpose):
"If you have a very large screen and a narrow spacing between your left and right speakers you can get all three behind the screen. The advantages of this include better concealment (e.g. high WAF factor), and the minimal sonic effect that the screen imparts will be identical across your (hopefully) identical front speakers."
"What is the real world result from placing your speakers behind a Center Stage screen? If only your center channel is behind the screen, you will need to increase the volume of the center channel one to two decibels. If you have all three front speakers behind the screen, you will only need to trim your surround channels one to two decibels to match your slightly attenuated front soundstage. The qualitative effects of having a fabric in front of your speakers is that you will notice that brighter recordings are tamed down a little, with a slight loss of sparkle and air, because the attenuation is higher in the top octave."
I run Audyssey every time I change anything with my audio. Typically, the default curve is the "House" curve, and this has a rolloff of the HF. Therefore with this screen, I expect that it will already do for Audyssey what it was going to for itself. So, In my case, I'm really not worried about this.
For you, if there is lack of "higher end" calibration going on, it may behoove you more to have all three behind the screen. OTOH, I fully expect that the difference will be minimal, if even audible (outside of level, but that's easy anyways), and more importantly, I think the benefits of a vertically arrayed center speaker placed as it should be, all drivers on the same plane, best possible acoustic match, best horiz dispersion, yada yada, will all far outweigh the aforementioned issue.
Paint. Whatever color you pick, even white for example, you will have to research online and hopefully choose the correct people to trust (don't ask me how I know), or for best due diligence, you get a variety of paints, and put them all side by side on a board. After drying, just look at all the samples under a light source, and you will see which are the most reflective, and which are the least. Otherwise, the darker the better, but you already know that.
What you might not know is that it is the ceiling that is generally referred to as the most important boundary of all to treat for light. However, while this is said in the general sense, it is assuming the type of screen which is generally used, and that is angular reflective. If OTOH it was the Dalite HP I mentioned before, it would instead be the back wall, generally speaking.
Back to speaker placement, and viewing angle, I'm glad to see that Seymour pretty much advises what I have found to work best on my own. Greater spread, with more extreme toe in (he advises even more toe in than I use), and well I'll leave the viewing angle alone for the moment, but mine pretty much is in line with his recs, topping his max rec by a couple degrees, but you'll see him say that is more workable when sources are HD, or with stricter light control, and mine has both.
Crap, I almost skipped it, but the 6" from ceiling, no I don't think it's an issue at all, except possibly* if you have a bright colored ceiling. I dunno. Mine as white wasn't too bad, but that's also because it is unlike 99% of the screens used in HTs with its reflective properties. You'll probably be just fine, and I don't even need to repeat this, but you should figure out a darker paint that the wife will like, that is also the most matte/flattest possible. I might even myself take a lighter colored paint that is less reflective, than a significantly darker paint that is more reflective.