From my experience. If you look at a turbo button with turbo plug installed, you can see the dome plus plug is a beautifull fit for good combustion.
Generally also Turbo plugs are hotter plugs and from my OS Vspec experience, I always had issues with the P3's. After about 1.5 to 2 litres the plug starts to lose performance and needs replacement. No ways you can tune it right.
What I do now is use standard buttons, I polish the chamber and make sure the plug makes a nice fit in the chamber without protruding or being in too deep. For me this works magic. Its like I am simulating the turbo button effect.
I cant see any noticeable difference to what I do to my standard heads versus the turbo head.
Mark share your experimentation with heads. I think you will agree you can get the same from a standard button if polished.