Hey Tijs,
I confirm that it doesn’t change. This is because of specificity. The h1 in an archive page has the class .h-landmark which has a set line-height in all the Stack’s CSS. Not sure if this is the intended design or is a bug but I’ll forward this to our dev team.
The Customizer setting will work on regular headlines.
To change the entry-title letter-spacing, add the code below in your Appearance > Customize > Custom > Global CSS
.h-landmark, .entry-title.h-landmark {
letter-spacing: 1em;
}
Thanks.