From what I have seen from Stratasys machines, the best spot for a chamber heater is hot air flow right at the nozzle level–this keeps the plastic warmer for a longer period of time, increasing inter-layer bond strength and reducing warping potential. This method is probably most effective when you’re dealing with high chamber temperatures and do overhangs with support materials; in fact, some Stratasys machines only rely on powerful chamber heaters (and no heated bed) to print plastics like PEI and polycarbonate
Seriously, look at Stratasys machines, they’ve been printing ABS for decades and have a lot of actual science behind their machine designs. What they do is heat the chamber to about 20-25C below the glass point of the material, and then use LOTS OF AIRFLOW on the print to get crisp detail. That’s optimal because it makes the plastic solidify rapidly without over-cooling it and causing warping.
The hotter your heated chamber, the more airflow you need. Consider this fact: PLA’s optimal “heated chamber” temp based on its glass point is basically room temp. (Maybe a little warmer at 30C.) It needs lots of airflow to print well. Likewise, any other filament in the proper heater environment needs lots of airflow.