New canes come from base, if you keep cutting off new shoots appearing there you will be preventing plants from replacing old stems. Also, usual problem with non-dwarf nandina is tallest, oldest canes becoming bare at bottom, as well as floppy. With a normal procession of replacement canes coming from bottom plant often well enough furnished for falling of oldest leaves from lower half (or more) of oldest canes to not matter so much. With newest, shortest basal growths kept pruned out there will eventually be nothing to hide bare legs of oldest stems. Your plants may start to look like palm trees.

If your main view of the stone work is the one in the first photo, it looks like a path. The view from the other side is more attractive anyway, as you can actually see some stone.

I'd prune out a few of the oldest, largest canes occasionally if you want to control size, otherwise leave them alone. They'll have a more natural and graceful form that way. IMO.

It looks like 2 votes no prune to 0 votes prune so far. Saypoint,
The primary view is actually from the left beyound the border of the first picture (a seating area and walkway). There is also a stepping stone path just to the right of the second picture.

I do want a small path to be along the nandinas that you see in the first picture. As I complete the other portions, I will have additional pictures for suggestions.
Thank you for your input.

In my experience the camera tends to flatten out topography, so it may look better in person, and also in my experience, there's not a darn thing you can do to make your stonework face you if your property slopes downhill from your vantage point. What we did was create a destination at the bottom so that we and visitors would at least sometimes be looking uphill at the more interesting face of the stones.

Karinl-I agree with your statement about stonework from above. With that in mind I laid the final course parallel to the hill so it would be more revealed. Also, there is an entrance to the Japanese garden from downhill (the approach shown in the second picture) to encourage entrance and discovery. Thank you.

Some thoughts to mull over.
One of the general acceptances of Japanese gardening is that even the smallest garden should have two entrances placed in the enclosure shrub/fencing. One is the principle entrance, the other a smaller back entrance. Nandina does become top heavy in time, sprawling outward especially when in fruit. Have you thought of moving them to the outside of the stonework and building a simple garden gateway somewhere within the Nandina shrub enclosure which would lead to whatever you plan to do beyond against the woods?

If this were my garden....I'd push the nandina further back from the wall ( 5-6 ft) and stagger them in a more irregular pattern (not in a straight line) to look more natural....more befitting the style of a Japanese Garden. That would give you space under and in front of them to put smaller, low growing plants that would enhance the wall. You then wouldn't need to prune them at the base.