I think you have a misunderstanding of economies of scale.

There are two ways of achieving economies of scale:

1. make things bigger

2. make more of them

Making things bigger generally is more effective when n is small. You need fewer sites, fewer approvals, each of the steps in the process is done fewer times.

When n is large, you can build and optimize a factory for them and achieve economies of scale that way.

Nuclear plants got large to take advantage of economies of scale because n is small. Nobody's building millions or even thousands of SMR's.