Manifold questions... slits on top or bottom?

OK, just going through some other threads and saw the picture in the How to Brew website (http://www.howtobrew.com/appendices/appendixD.html)...

Have people tried both top slits and bottom slits? I see the upward facing slits as the most common, but to me it seems this is suboptimal because:

- It leaves more liquid in the bottom of the tun. Even if piping is flush to bottom, a good 1/2" or wort could be lost (if the area of the tun is larger, this could be more significant)
- The liquid will flow in either method as the saturation of the grains at the bottom is a given, so as water is added above, the pressure of this water forces the wort below it to drain, it seems to me this would be functionally equivalent

Only hole in this logic I see is that the liquid along the bottom may flow more freely along the bottom wall of the tun, but I have no practical experience that shows that to be true...

Anyone else tried these methods and have an opinion or is it just accepted as fact that you need your drain slits facing up?

Slits on bottom = less dead space. My CPVC manifold is set with bottom facing slits without problems.

+1
top is grain and grain flour. Bottom is where the liquid is...