We're finding that our structures really don't need to be over 3 foot tall as the largest slabs seem to always be near the bottom. Why make them easier for people to snag them and possibly hit them during low water and damage the stakebed.
If we put any Bamboo out though I'll probably still go with the half the water column as a general rule. Seems to work pretty good.
Here's a few that I helped NIMROD build a while back. He has a lot of these out now. Expect him to posts some real nice slab pics this year.