yes the b6hs has a slightly lor reach than the stock china plug.
BUT, if you remove the head (I'm referring to a slant head here) and look at how far the china plug screws into the head, you'll laugh.
The china plugs electrode is actually shrouded by the head because it doesn't reach into the combustion chamber far enough. yes, it works, but you are loosing a little spark energy because it's shrouded by the head.
The b6hs will reach into the combustion chamber a little further, won't be shrouded and will actually give you a SLIGHT gain in power and a better idle because the fuel burn is better.
just be safe and put the plug in it, and turn it over by hand. it shouldn't hit the piston, but you never know.
it's better to be safe than sorry.