In my experiences, the tail is not included. It is considered "bonus" footage. This is also common with oddly shaped gamerooms. Our MLS input forms only allow for a square measurement and this can be quite frustrating when there is a great deal of oddly shaped bonus area. However, I was always advised never to overmeasure and always round down. Buyers will never complain about extra space, but they will get very upset if they get less space than they were quoted.
I answered a similar question you posted earlier and I will reiterate here: If you do this - use any & all floor space/living space as you like.... you see - it doesn't matter because you can't use the numbers in selling your home.
For one - they are at best considered "guesstimate" and if you write it down on any marketing or advertising you will be held accountable for the final numbers. If they are off - you stand a chance of losing the deal based on faulty information.
So, measure away - but if you provide the totals - make sure you tell them they are at best a "guess".
Your profile says you are a real estate pro, is that correct?
The first law of real estate is don't perform services outside your area of expertise. In some states local custom is that the Realtor measure the property.
My Loss Prevention training in Keller Williams is that would you be better served to have the property measured by a professional with expertise in that job. Should there be a discrepancy in the measurements a third party would bear the brunt of the error, not you. Plus, they usually provide a handy property layout that you can put on your flyers (with the correct disclaimers of course), and upload to the MLS.