Seems the LMB have lots of food and might not be that active because they do not need to be. I think SMB tend to be more school oriented and have a less lazy feeding pattern than LMB, perhaps thats why you are seeing SMB. The LMB probably are just hanging around a structure and picking off something when they are hungry.

Goofing off is a slang term for engaging in recreation or an idle pastime while obligations of work or society are neglected........... Wikipedia