Plug readers

Stock heads or aluminum? Reason I ask is that I have the stealth440 heads and used their recommended plugs which had the 3/4 long threads and they always looked like the example you provided. Went to a hotter plug which has the 1" long threads and they looked 100% better with no carb or timing changes. Conclusion is the plugs were hidden in threaded shaft instead being exposed at the end of thread shaft.