Pre-heating laser for better results

I am having issues when I try and engrave one of the demo aluminum business cards where it doesn't look like it was powerful enough on a bitmap portion. The text all looks great but the bitmap is slightly faded. I attempted to increase power and that helped a bit. What is the best way to deal with this? Adjust the speed for bitmap and increase speed? Or in the manual it mentions pre-heating laser first? How do you do that in the software as it is not mentioned in the manual that I saw?