I don't have tables or charts in front of me but I doubt that you going to be really dealing with a high enough flow of gas (smoke) to make a turbulent/laminar difference. If anything, adding some angle iron down there will have much more of an impact as a thermal mass than anything else. Granted it has been a few years since I've taken fluid dynamics and heat transfer but I'm pretty sure about this. Sure, baffles will slow down the flow of the hot gas and also act as a heat sink in reverse but I'm not sure a few pieces of angle iron would noticeably improve efficiency. That is assuming you are defining efficiency as the amount of fuel burned for a given period of time.
Best way to know for sure is to try though, worst case scenario is that you have more thermal mass to help with recovery.
Hope this helps