Well I think it is because you have to complete a short form for each submission, why it is submitted and brief information on why.
I don't know if you zipped the samples together and then add the zip file to the chest manually, you could then send the zip file for analysis as undetected malware samples.
Other than that you can, send the sample to virus (at) avast (dot) com zipped and password protected with the password in email body and false positive/undetected malware in the subject, plus any additional information you have.
