I would step up a little for those ceiling speakers.......Not a huge amount, but a couple levels from those, especially with your proposed locations.
I am running 7 matched speakers, so the ceiling speakers have 2,6.5 woofers and a horn loaded tweeter.
If you are not going to put those speakers almost directly overhead, they will have some directivity issues,especially with a non pivoting tweeter.
Mine are front main width and approx. 20 inches in front of my ears and I had to give them 6db of gain just to get them to blend with a 8 foot tall ceiling.......I have moved them a couple times now and will be locating them a little closer together and a little closer to directly overhead.
The dolby set up states to approx. keep them the same width as the mains, the whole equilateral triangle thing, but I believe they work better if you use the equilateral triangle based on distance from your ears to the ceiling.
Something like this....... https://www.parts-express.com/bic-ac...eaker--303-484
It has a 8 inch woofer and a pivoting tweeter, and is still affordable.......
I have a entire Bic system and it sounds pretty good, it is certainly not Martin logan vanquish quality, but for the price, they get the job done.
I would also consider some sort of switch like you propose and consider getting 4 of those bic speakers in the ceiling, a little in front of your seating position and a little in back of the seating position.....with approx. 6 foot spread to center you in the ceiling soundfield.
You might already have some small cheap speakers, but I would put some overhead and move them around first before mounting those in ceiling speakers........or see if there is a small hole in the in ceiling speakers and move them around on the ceiling first before cutting them in to see what you prefer.
That dolby atmos layout has a lot more flexibility than you would think.........my speakers are about even with the front of my seats,so 20 ish inches in front of the ears and since they have no directional/pivotable tweeter they need to be 6db hot to just blend, I might bump them up another db until I move them another 6-10 inches closer to in line with my ears.
As mentioned above, also moving them closer together and centering them off the seating, rather than the room as they also seem very sensitive to width location with a non directional/pivoting tweeter.......the pivoting tweeter should help with that in your case, something I would seriously consider in a ceiling speaker that will only be approx. 48 inches above ear level..........Imagine how directional it would be if you sat 48 inches back from your mains....
Also biology has a little say too.....
we are designed to hear on a ground plane,our ear shape is conductive to that, it is not shaped well to pick up over head sounds.........next time you have the stereo on, set it for 2.0/2.1 and while the music is playing take your head and point it at the speakers looking straight down at the floor and see how much it changes.........
Sorry for the long post, but these are just some observations I have made playing around with the Atmos overheads over the last 6 months.
From mine and other peoples observations in my room with the different speaker locations on the ceiling seems to be 24-36 inches in front and behind the ears, with a pivoting directional tweeter to be a highly desirable feature. And with most people crossing over around 100hz, as large as possible woofer up there to get that 100-500hz bass overhead.
2, 6.5 inch woofers that I have is about the same as a single 8 incher for bass and I feel a little more punchy bass up there in 100-500hz would not be a bad thing, but they seem to be enough to do the job. I imagine a pivoting tweeter would give a little more wiggle room up there, but with a fixed tweeter they will be very location dependent/sensitive.
Some of the better designs seem to feature multiple directional tweeters......but those fall outside what I am willing to pay and I believe a 8 incher like the bic with a directional single tweeter will do 98% of what the more expensive multiple tweeter designs will do, with a little time spent getting that ideal location.
Keep in mind this is for a single row of seats, I am sure 2 rows will change things...........