John,
While it may be fun to try and mount the W's upside down (houses & gravity aside \:\) ) I can tell you that they sound great mounted 'traditionally'.

I have my W150 mounted below the screen and the W22's mounted so that the bottom of the speaker is in line with the bottom of the TV which puts the tweeter about mid-screen height wise. I personally do not notice any issues with the center channel tweeters being lower than the L & R's.

Dan
On-Wall M5HP LCR, QS8 & EP500 in 7.1