Modified cox 049 glow head
Yep, you'll get a power loss even after you trim the recess to let the plug sit at the right depth. It's mostly related to the little ridge. Fine for sport flying if your models aren't meant for speed though. With them down where they should be you'll loose about 800 to 1000 rpm if I remember right.
Some control line speed guys did a few heads with a flat bottomed blind hole so the regular plug just barely touched the base of the threaded hole as the gasket tightened. The idea being to keep the shape of the high compression trumpet plug. Worked pretty well but the fit was critical and the plugs weren't the same size between brands to that tolerance. Net result? Very mixed performance depending on the plug and gasket fit.