Now flat corners you lean the bike but keep yourself upright and weight the outside pedal don't you? That way the knobs on the outside of the tyre dig in.
But on berms, the berm itself leans the bike so I presume you stay vertical on the bike ie: keep your body perpendicular to the berm to maximise grip through the bottom of the tyres.

depends on the shape and size of the berm.

if you can get pedals level you can pump the berm better.

http://www.5min.com/Video/Bikeskillscom-Pump-Track-Fundamentals-11257582

That is a good web site….

Depends on the berm, for big open ones (eg Bary knows best) I just treat it as a normal corner, outside foot down, inside foot hovering over the pedal ready to dab if needs be.

Really tight ones (The labrynth at Swinley) there's absolutely no way of loosing grip, just a case of how much bottle you can give ti and how hard you can pump out of them.

Watch f1rst, hypnosis, synopsis or any other MTB films based arround DH racing for a better idea.

If you hit the berm at the perfect speed/height on the wall, then pedals level and both you and the bike lean to the same degree.

Go faster than your position on the berm "allows" and you may have to lean the bike more than yourself and/or drop the outside foot as in a flat corner.

Otherwise, look for the exit and pump for speed!