The hot face should be about 2″ from the garment. This is a very rough rule of thumb. To get a faster flash you can move the panel hot face closer. To reduce the heat on the garment to prevent overflashing or overheating the shirt board, move the heater back away from the shirt board. It’s common to require less heat to flash when the shirt board temperature increases with production. You may want to consider a temperature control for the flash heater to avoid having to raise and lower the heater during production.