Unfortunately, the probe looks for exact string in subject, no regex search is implemented in it.
However, I did couple of tests with gmail account, and when I set forwarding on the gmail server, I don't see any 'Fwd:' prefix in my forwarded messages.
I don't know, how your mailboxes are configured, it seems that you set up the forwarding rule on your email client. Consider creating dedicated gmail account with forwarding to the monitored mailbox for purpose of EWS monitoring.
