Understanding Simple Static Meshes and why they are not shading correctly

I have created a series of walls and floor tiles.

The wall segments are 300 high and 140 wide. The floor times are 140x140.

I am currently getting poor shading when I use the walls with the floors but I cannot figure out why.

In this example, you can see I have 5 segments of wall with 5 tiles of floor. There are incorrect shading on the joins (which they are all using the snap grid 10 value)
I have run a build at High level but you can clearly see the joins still

If I then remove the floor and rebuild, it appears the walls look much better.

And then If I add a bsp floor below the walls it appears to still look good.

These meshes were built in the latest blender app using a metric scene of 0.010 scale. The UK is a straight forward Smart UV with a Island Margin of 1 and an angle limit of 66.00
Any suggestions will be much appreciated.