I had to modify my router fixture 'base' to accommodate the smaller shelf widths that I now have (compared to the others I did at the beginning). To start with, I unscrewed the bottom piece and turned it around (notice the notch is now facing down). The reason is two-fold: First, like I said before, the small bottle shelves are not as wide now, so I had to move this piece 1/4" to fit my new width. And second, the existing notch that you see below was too large so I'll have to cut a new one of the correct size.

Notice the piece of white paper between my small bottle shelf and router fixture. I clamped all these pieces together and then screwed that bottom piece to the base. Once I removed the piece of paper, this gave me the perfect amount of clearance between the two surfaces.
 

Here is the result, four slots that are exactly the right size. But now it's time to cut more material from each slot so it will fit the smaller bottle.
 

And yet another router fixture. This one will be used to cut an angle on the under-side of the shelf. This angle will be 45 degrees and will provide clearance so the bottle will fit into the slot. The arrows are pointing to the new slot width that I needed for my 45 degree router bit. This slot width matches what I just put in the shelves in the previous operation.
 

Here is a view of the top and bottom of the shelves. Now I need to put a small recess on the top surface so the bottles stay in place, like I did for the larger bottles.
 

After doing some measuring, the small and larger bottles are almost the same size where the recess is concerned. This is good news because I can use the router fixture that I made for this earlier.