What??..... 2 layers.
As far as we know this the only config.
Look at your first image with the truck mounted 9M96 (the full length tubes) and the 9M100 (the short tubes).
In your pictures showing the 9M96 missiles lying next to the full sized 40N6 missiles you can see the 40N6 is as wide as the four pack of 9M96 missiles, so if Redut can carry the 40N6 missile it must be both wide enough and long enough to fit that rather big missile.
If Redut can fit the big long range missiles then it should be able to fit four of the 9M96 missiles in the same space because they were designed to fit into the same space... there are pictures of S-400 missiles with one large missile missing and a quad pack of 9M96 missiles in the one missiles place.
The S-350 is not designed to carry the big 40N6 missiles as it would need to be rather longer to fit the wider and longer missiles.
If Redut can carry the 40N6 missiles then there must be extra length space within the tube to fit those longer missiles.
Now look at the S-350 launcher again... the 9M100 missiles are rather smaller than the 9M96 missile tubes.
The 9M96 tubes are not half the length of the 40N6 so you could not stack them in Redut, but the 9M100 missiles might be half the length of the 40N6... we know they are a quarter the size so even with just one layer they could have 16 missiles per 40N6 tube... the question is can they fit 32 in two layers of 16 missiles.
It is not really critical for Redut, but for bigger tubes like UKSK-M stacking might solve the problem of volume... tiny missiles are not worth carrying if you can only carry one in a huge tube... it is all about efficiency of using the tube... getting four 9M96 missiles into one tube means you can have extreme long range with one 40N6, or you can give up that extreme range... which many targets wont warrant anyway and get four shorter ranged missiles.
In fact you could mix it up and have two 150km range missiles and two 60km range missiles... or you might even have one 150km range missile, two 60km range missiles, and four 10km range 9M100 missiles under the one Redut hatch cover...
If the 9M100 can be stacked then you could have 8 x 10km range 9M100 missiles... which is even better.
The UKSK-M has to carry enormous long range cruise missiles 10m long and also the S-500 which could be an enormous missile too, which means the tube is even wider than the redut tube... there is little chance of getting two or three or four 40N6 missiles in each tube, but their might be room for more 9M96s and certainly regarding length there should be room for three lots of 9M100 missiles stacked on top of each other... it is just a way of more efficiently using up space.
Now this is all assuming Redut and the S-350 have the same dimensions.
Look at the big tube at the back on the truck mounted S-350... that is the 9M96.
That is the missile on Redut which has a fairing all round it because the hatch cover is enormous... and it has to be that big because each cell is designed to carry 40N6 sized missiles which your posted images above clearly show in the background is rather bigger (wider and longer) than the 9M96.
The 9M100 is even smaller and can fit in the space of one 9M96.
It is like the Russian dolls... the Redut launcher on the ships can take the 40N6... if you open that you can fit four 9M96 inside though there is a gap because they are rather shorter than the 40N6. If you open each 9M96 you can fit four 9M100 missiles in each.
That means that a single Redut launcher cell (ie each hatch cover) can be loaded with one 40N6 missile, OR four 9M96 missiles, OR 16 (4x4) 9M100 missiles.
That seems to be fact.
What I am suggesting is that the 9M100 missiles are so much shorter than the 9M96 missiles and also the even bigger 40N6 that fit in the tube that it might be possible to stack the 9M100 missiles in two layers... so 32 missiles per tube instead of 16.
This would be very useful for small vessels as the 9M100 practically equates to a very high performance CIWS anti missile missile.
The latter is purely speculation on my part and I have no evidence or have seen no references to suggest I might be right regarding stacking.
The UKSK-M would benefit enormously from stacking of different missile types as it is designed to carry a wide range of missile sizes (widths and lengths).