Currently global housekeeping settings override item settings for history/trends.
That's good to have in case you set to keep item history for a year, but global history is set to for example 1 month. This way database won't grow huge and history will be truncated.
But if we set small item history (for example, 7 days) and global setting is larger (for example, 1 month), global setting still overrides item setting:

IMHO better way is to override item settings only when item settings is larger than global settings.