Yes, you are allowed to file 6 months prior.
Without knowing more, to optimize, you must know that USCIS will take 4-5 months to adjudicate the COS application. Leaving the country during the pendency of a COS application will be deemed as an "abandonment" and your application could be denied as such. You will then be deemed to have been out of status and started to accumulate "unlawful presence" as of the date of your I-94 expired.
Knowing what you now k ow, act accordingly and decide what is "optimum" in your situation and objective you are trying to attain.
Behar Intl. Counsel 619.234.5962 Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
Likely USCIS will not grant more than 6 months. And if you think you need several months to wrap up your affairs and you understand that CIS will take 2-3 months to adjudicate the matter, then plan accordingly.
B2 will be allowed 6 months but how much time you ask and finally get depends upon your need and how you show this especially after stayng on L. Best Wishes!
Attorney: Immigration Law
13295 Illinois St Ste. 128
Carmel IN 46032
Ph: (317) 660-6174