Thank you for providing those screenshots. If you use the option 'Leave message body in the stub', it is recommended to also use the 'collect only messages containing attachments' option. This configuration would leave the message body viewable without recalling the message, but would only archive messages that have an attachment. If you have the 'leave message body in the stub' option enabled, and archive a message that has no attachments, you will not see a size reduction as there is not really any data being removed from the mailbox (as we are leaving the message body behind). In fact, in that scenario you can see the message size increase as we are adding metadata (stub identifier, etc) to the message.
Please let me know if you have any questions, or if any further clafication is needed.
WW Support Expertise Team