That's probably it Cam, maybe a broken ring during break in. Its a pain to stick the piston in the jug and hold the rings where they are supposed to be, especially if you do it alone. Something is in there. You might as well pull off the top, because no matter what it is, it has to come out. The head has a domed combustion chamber, like cam already pointed out, so the plug would never hit the piston.
Whats the leak down test going to show on new motor? If it leaks off compression, wouldn't it still need a visual inspection and repair? If it doesn't lose any, wouldn't you guys still have to pull off the top end to fix it, no matter what is causing it? Seems like that test would only confirm there's a problem, when that's obvious. What would that test tell BMH about the cause?