vic, nice analysis. A bat tail though, is not the best option for a bodyboard in big surf. Generally, bat tails are used in smaller surf as they are 'looser' than the crescent tail. The crescent holds the wave much tighter than a bat tail in big, hollow conditions.
Honestly, it really depends on the conditions, the rider, the way the wave is breaking, etc. Is the wave a spilling or plunging wave? Is the wave closing out quickly or do you have some time to maneuver? All of these variables depend on the break and what that particular beach break is doing. I have used bat tails in overhead surf, as well as smaller shorebreak with good results.
The best bet is to simply bring a variety of boards so you can be best prepared for whatever the local break is going to throw at you. I will be bringing (1) bat and (2) cresent tailed boards for this surf..