How do you find custom activities without attachments

I'm using Dynamics CRM 365 Online and the advanced find to try and locate all "custom" entity records that DON'T have a file attached.  I can locate the ones with attachments using the Note(Regarding) > File Size (Bytes) Is Greater Than or Equal To 1.  BUT if I change it to Is Less Than or Equal To 0, I get no results.  I know the activities exist because I created some test ones with attachments.

What am I doing wrong?