If the header pane above the message view is disabled, Claws has a config option for not displaying (X-)Face. But if the header pane is enabled, the config option is greyed out, effectively removing the choice of displaying xfaces from users who are using the header pane. Suggestion: replace the checkbox with dropdown gadget, giving three options for xface display: message view, header pane, not displayed at all.
Actually, I would suggest making this option simpler: [ ] Display Face if possible. And if its enabled, show in both header and message view, and if it's not, don't. IMHO it's such a trivial option, it should be "enabled" by default and moved to be a hidden preference.