This is probably a ridiculous thing to even mention, but is it for sure a heat gun that you're using, and not a blow dryer? I'm only asking because I've seen others get confused, not to try to be insulting... You could also try heating the embossed image from underneath, so there's no air flow onto the powder. "Back in the day" before heat guns were widely available, we used to hold the paper over a light bulb or toaster to melt the embossing powder - no blowing at all - so you could try that if you got desperate.
I'm blogging again: random.on purpose.
Within you there is a solitude and peace to which you can retreat at any time and be yourself...