Couldn't reproduce "Core increases minor heap to 8 MB"

[leviroth]

Chapter 24 says:

The default minor heap size in OCaml is normally 2 MB on 64-bit platforms, but this is increased to 8 MB if you use Core (which generally prefers default settings that improve performance, but at the cost of a bigger memory profile).

However, the minor heap size on my 64-bit system appears to be the default 262144 words, i.e. 2MB.

$ cat bin/main.ml
open! Core

let () = printf "%d\n" (Gc.get ()).minor_heap_size
$ dune exec bin/main.exe
262144

It wasn't clear to me if this information is stale, or if there are some further preconditions beyond merely using Core that are necessary to change the heap size.