I don’t think “one artifact, one vote” is a fair way to measure this.

One reason builds become irreproducible is when a build is multi-threaded, and the order in which artifacts are combined into larger ones becomes unpredictable. That problem doesn’t exist, or at least is a lot smaller, for ‘leaf’ artifacts (example: if your C compiler is single-threaded, and you run make multi-threaded, individual object files do not have the ordering problem, but libraries built from multiple object files do)

On the other hand, a single static struct with a padding “hole” that isn’t consistently written that happens to end up in lots of binaries will decrease your percentage a lot.