Even with no spaces in the config format string, it appears there are three spaces between the mpris buttons.

Quick solution.
py3status --include ~/.config/py3status/modules.mpris.py with this diff.min_width to your likings. diff --git a/py3status/modules/mpris.py b/py3status/modules/mpris.py
index 8c2705c..cad64dc 100644
--- a/py3status/modules/mpris.py
+++ b/py3status/modules/mpris.py
@@ -303,7 +303,7 @@ class Py3status:
"color": color,
"full_text": control_state["icon"],
"index": button,
- "min_width": 20,
+ "min_width": 10,
"align": "center",
}
Thanks!
Closed via #1738.