When you print small things or difficult hoverhang you rapidely realise that a good ventilation is critical. But blowing directly on the J-Head created to much cooling of the head itself. Following some advices I recived I went for insulation of the tip of the hotend. I went for blue silicone liquid seal (can be found in any automotive store) as it can whistand 250°C peak temperature. Apply the silicone generousely aroun the hot tip of the hotend, it should cover averythong the thermistor, the heating element with a layer of around 3mm thickness to insulate well. That's it you now have a well insulated hot-end! Do not forget to recalibrate the PID parameters for the HotEnd because with the insulation these will be different you can use the following gcode "M303 S197 C8" as described in http://reprap.org/wiki/PID_Tuning I've included my config.h where the PID constants are stored.